Calibration Report 1.20 · 2009. 4. 28. · NOTE 3: Each oven and shield has its own R0. These...

PHOENIX MARS LANDER 2007

THERMAL AND EVOLVED GAS ANALYZER

CALIBRATION REPORT

Version 1.20

4/22/2009

- 1 -



CALIBRATION REPORT

Version 1.20

4/22/2009

Prepared By:

TEGA TEAM



CALIBRATION REPORT

Version 1.20

4/22/2009

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Table of Contents

1 Background ..............................................................................................................................3

2 TEGA Engineering Subsystem ................................................................................................4

2.1 AD590 Temperature Sensors ........................................................................................... 5

2.2 PRT Temperature Sensors ................................................................................................ 5

2.3 Engineering Voltages and Currents.................................................................................. 7

2.4 Status Channels ................................................................................................................ 8

2.4 TA_MANIFOLD_PRES (0), TA_OUTLET_PRES (2) .................................................. 9

2.5 Oven and Shield Error Signals ......................................................................................... 9

2.6 TA_T_HEATER_TEMP (23) ........................................................................................ 10

2.7 Oven and Shield Voltage and Current............................................................................ 11

2.8 Pulse Width Monitors..................................................................................................... 11

2.9 TA_FULL_DETECT (42), TA_FULL_DETECT_RAW (43) ...................................... 12

3 Calculating the Calibration Curves for the Oven Pt Sense Winding ....................................13

3.1 TA0: ............................................................................................................................... 15

3.2 TA1: ............................................................................................................................... 16

3.3 TA3: ............................................................................................................................... 16

3.4 TA5: ............................................................................................................................... 17

3.5 TA6: ............................................................................................................................... 17

3.6 Further Discussion.......................................................................................................... 20

4 Converting TEGA DSC telemetry to true power ...................................................................22

5 Pressure Transducer Calibration ............................................................................................24

6 EGA Mass to Voltage Conversions .......................................................................................27

6.1 Theory ............................................................................................................................ 27

6.2 Practice ........................................................................................................................... 28

6.3 Calibration (coefficient derivation) ................................................................................ 28

6.4 In-Situ Calibration .......................................................................................................... 30

6.5 Ground Data Reduction .................................................................................................. 33

6.6 References ...................................................................................................................... 33



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1 Background

Phoenix TEGA is part of the instrument package onboard the 2007 Phoenix Mars Lander.

The Phoenix mission, the first chosen for NASA's Scout program, began exploration of

the Northern plains of Mars during 2008. TEGA stands for Thermal and Evolved Gas

Analyzer and is directed toward sampling and understanding the chemistry and

mineralogical components of the soil through thermal (heat capacity) and gas analysis of

soil samples delivered by the Robotic Arm from various sampling locations beneath and

beside the Lander. An additional capability is using the Evolved Gas Analyzer to

measure trace components of the Martian Atmosphere. A detailed description is

contained in the TEGA Instrument Paper (Boynton et al 2008) but a brief description is

presented below.

TEGA has three major components: The Control Electronics (CE); the Thermal

Analyzer (TA); and the Evolved Gas Analyzer (EGA). The control electronics (CE) is

enclosed in a payload package beneath the Lander deck and contains a microcontroller

and power conditioning and control system as well as a housekeeping component. The

housekeeping component measures currents, voltages, pressures, and temperatures of the

various sensors scattered over the instrument. The Thermal Analyzer sitting above on the

deck receives the sample from the Robotic Arm seals it into an oven and runs a

calorimetry scan under control of the CE. The TA is also supplied with two gas supplies

and valves to route the gas from the supply tanks and eight ovens to the EGA. The

Evolved Gas Analyzer is a 4 channel magnetic sector mass analyzer that measures the

concentrations of gasses either from the ovens or the atmosphere.

The primary purpose of this document is to provide the critical information required to

convert the raw data from the instrument into standard units corrected to the degree

possible for the understood effects of environmental and instrument behavior. Some of

these conversions were calculated in-situ in real-time with the majority taking place as a

post process to the receipt of the data on the ground.



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2 TEGA Engineering Subsystem

The TEGA Engineering Subsystem is based on a radiation hardened Analog Devices

AD7872 A/D converter. This is a signed, 14-bit converter with an input range of -3V to

+3V. A summer at the input to the ADC is used for level shifting, allowing the system to

process input signals of 0 to +6V, -3 to +3V, and 0 to -6V (Figure 1).

Figure 1: Analog Signal Processing

Figure 2 shows the transfer function of the ADC. The TEGA flight software converts the

ADC output to a signed, 16-bit integer using the rules in Table 1.

Figure 2: ADC Transfer Function

Input Range Conversion

0 to +6V Invert bit 13

-3 to +3V Sign Extend by copying bit 13 into bits 14 and 15

Ch

an

ne

l S

ele

cto

rP

ola

rity

Sele

cto

r+3V

0V

-3V

+

-G=1 ADC

Ch

an

ne

l S

ele

cto

rP

ola

rity

Sele

cto

r+3V

0V

-3V

+

-G=1 ADC

Ch

an

ne

l S

ele

cto

rP

ola

rity

Sele

cto

r+3V

0V

-3V

+

-G=1 ADC



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0 to -6V Invert bit 13 then subtract 0x3FFF Table 1: Converting ADC output to signed, 16-bit integer

2.1 AD590 Temperature Sensors

Most of the temperatures in TEGA were measured with Analog Devices AD590

temperature sensors. These sensors pass a current that is proportional to the temperature,

with a nominal slope of 1µA/ºK and absolute accuracy of ±1.7ºK from 218 to 423ºK (-55

to +150ºC). All of the flight sensors were tested for linearity down to -100ºC. The

excitation voltage for the sensors was +12V, and the output current was read out with a

15.4K, 0.1% resistor, resulting in a nominal voltage to the ADC of 15.4mV/ºK

(42.08dN/ºK). Each readout channel was characterized before launch with a precision

current source, and the results are shown in Table 2.

Name (Channel #) Location A B

TA_MANIFOLD_TEMP (3) Valve manifold in the TA 42.0347 -273.470

TA_PLUMBING_1_TEMP (6) Plumbing between cal tank and valve manifold

42.0385 -273.470

TA_PLUMBING_2_TEMP (7) Plumbing between valve manifold and transfer tube junction

42.0357 -273.463

TA_CAL_TANK_TEMP (9) Cal gas tank near heater 42.0411 -273.441

TA_CAL_TANK_COLD_TEMP (46) Cal gas tank at coldest spot 42.0345 -273.469

TA_TRANS_TUBE_TEMP (24) Transfer tube between TA and EGA

42.0366 -273.458

TA_EGA_MAN_TEMP (8) Valve Manifold in the EGA 42.0335 -273.505

TA_EGA_PLUMB_TEMP (4) EGA plumbing between transfer tube and ion source

42.0361 -273.473

TA_CPU_TEMP (10) FPGA-A, the hottest component on the CPU board

42.0383 -273.475

TA_PWR_SPLY_1_TEMP (11) Thermal plate near shield power converters

42.0362 -273.479

TA_PWR_SPLY_2_TEMP (12) Filter board near linear optocouplers

42.0336 -273.496

TA_PWR_CNTL_1_TEMP (13) Center of thermal plate 42.0330 -273.487

TA_PWR_CNTL_2_TEMP (14) Power control board near oven/shield power monitor circuit

42.0355 -273.481

TA_A2D_TEMP (15) On the A/D converter on the analog board

42.0497 -273.150

TA_EGA_ELECT_BOX_TEMP (22) EGA electronics frame 42.0345 -273.465

EGA_PROC_TEMP (87) EGA CPU Chip lid 33.9252 -290.937

Table 2: AD590 conversions. Temperature (C) = raw / A + B. This assumes a perfect, 1µA/ºK sensor.

2.2 PRT Temperature Sensors

For locations where the temperatures to be measured were likely to fall outside of the -55

to +150ºC range of an AD590 sensor, PRT sensors were used. These sensors change their



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resistance proportionally to the temperature, with a slight nonlinearity. The conversion

for these sensors is done in two parts:

1) Calculate the resistance of the sensor from the raw ADC data

R = raw * M + N

2) Use a polynomial to convert the resistance to temperature

T = A + B * (R/R0) + C * (R/R0)^2 + D * (R/R0)^3 + E * (R/R0)^4

Table 3 gives the coefficients for the 6 PRT sensors, and Table 4 gives their locations in

the instrument.

Channel R0 M N A B C D E

TA_OVEN_TEMP (20) NOTE 3 -1.23000E-02 8.861305E-02 -237.547 222.581 16.5808 -2.21177 0.453123 NOTE 2

TA_SHLD_TEMP (21) NOTE 3 -1.22014E-02 8.786520E-02 -237.547 222.581 16.5808 -2.21177 0.453123 NOTE 2

TA_EGA_BAKEOUT_TEMP (5) 100 1.07748E-02 -2.99666E-01 -245.941 236.19 9.87813 -0.300534 0.176804

TA_EGA_GEC_TEMP (25) 100 2.31475E-02 -5.33560E-01 -245.941 236.19 9.87813 -0.300534 0.176804

TA_COVER_1_TEMP (16) 1000 9.10115E-02 -1.57889E+00 -250.948 239.505 11.8457 -0.661546 0.263552

TA_COVER_2_TEMP (47) 1000 9.09908E-02 -1.59992E+00 -250.948 239.505 11.8457 -0.661546 0.263552

TA_INPUT_FUNNEL_1_LO_TEMP (17) 100 6.79072E-03 -2.55897E-01 -245.941 236.19 9.87813 -0.300534 0.176804

TA_INPUT_FUNNEL_2_LO_TEMP (19) 100 6.78924E-03 -3.43167E-01 -245.941 236.19 9.87813 -0.300534 0.176804

EGA_MAGNET_TEMP_1 (85) 100 Note 1 Note 1 -245.941 236.19 9.87813 -0.300534 0.176804

EGA_MAGNET_TEMP_2 (86) 100 Note 1 Note 1 -245.941 236.19 9.87813 -0.300534 0.176804

Table 3: PRT conversion coefficients

Channel Location

TA_OVEN_TEMP (20) TEGA Sample Oven

TA_SHLD_TEMP (21) Heated Shield around the Sample Oven

TA_EGA_BAKEOUT_TEMP (5) EGA Ion Source Housing

TA_EGA_GEC_TEMP (25) Inside of the EGA GEC Getter mounting post

TA_COVER_1_TEMP (16) On the body of the North side cover actuator

TA_COVER_2_TEMP (47) On the body of the South side cover actuator

TA_INPUT_FUNNEL_1_LO_TEMP (17) Backside of the TA0 funnel

TA_INPUT_FUNNEL_2_LO_TEMP (19) Backside of the TA5 funnel

EGA_MAGNET_TEMP_1 (85) Main EGA magnet, Ion Source end

EGA_MAGNET_TEMP_2 (86) Main EGA magnet, Ion exit end

Table 4: PRT Sensor Locations

Note 1:

The two EGA magnet PRT sensors use a significantly different readout circuit. For these

two sensors,

+

−

+

=

G

FR

G

FR

S

R

RV

V

R

RV

V

RR

1

1

1

,

where V=raw/3276.6,

RS=3240,

VR=5,

RF=10000, and

RG=1000.



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Combining and simplifying, step 1 becomes

−

−

×= 1

1802131

13240

rawR .

NOTE 2: The sense windings in the ovens and shields are 99.99% pure Platinum wire.

The datasheet lists the α for this wire at 0.00391, making it distinct from the “standard”

Pt curves (0.00375, 0.00385, and 0.00392).

NOTE 3: Each oven and shield has its own R0. These values are given in Table 5.

Cell # Oven R0 Shield R0

0 35.0042 41.7947

1 35.6493 37.7694

2 34.3812 37.9078

3 35.0782 40.1532

4 33.9038 40.5646

5 35.7848 36.8087

6 35.3818 39.1227

7 35.4578 40.6081 Table 5: Oven and Shield R0 Values

2.3 Engineering Voltages and Currents

There are many voltages and currents that are monitored primarily to assess instrument

health and safety. All of these monitors use a linear, result = A + raw * B conversion. A

few of the monitors require some temperature compensation.

Channel A B Unit Description Note

TA_BUS_A_VOLT (26) -1.2206E-01 2.1520E-

03 V

Spacecraft bus voltage, measured AFTER the input filters,

i.e. as close to the actuators as possible

TA_BUS_A_CUR (34) 1.3978E-02 1.7019E-

04 A Bus A (RPC06) current draw NOTE 4

TA_BUS_B_CUR (35) -1.0190E-01 1.6997E-

04 A Bus B (RPC03 + RPC09) current draw NOTE 5

TA_EGA_CUR (36) -1.2316E-02 1.6712E-

04 A EGA PECM current draw NOTE 6

TA_CPU_PLUS_5_VOLT (29) -5.8102E-03 3.6635E-

04 V TEGA CPU board +5V rail voltage monitor

TA_CPU_PLUS_5_CUR (37) -1.7086E-05 9.1846E-

05 A TEGA CPU board +5V rail current monitor

TA_ANLG_PLUS_12_VOLT (30) 0 9.3206E-4 V TEGA Analog board +12V rail voltage monitor

TA_ANLG_PLUS_12_CUR (38) 0 2.39E-5 A TEGA Analog board +12V rail current monitor

TA_ANLG_MINUS_12_VOLT (31) 0 9.3206E-4 V TEGA Analog board –12V rail voltage monitor

TA_ANLG_MINUS_12_CUR (39) 0 2.39E-5 A TEGA Analog board –12V rail current monitor

TA_PLUS_5_VREF (1) 0 3.6623E-4 V Direct readout of a precision +5V reference

TA_PRES_SENSE_FD_BK (18) 0 7.3247E-4 V +10V reference to pressure sensors

TA_AGD_0_3 (27) 0 3.6623E-4 V Unused MUX input, tied to analog ground

TA_AGD_3_1 (28) 0 3.6623E-4 V Unused MUX input, tied to analog ground

EGA_ION_PUMP_VOLT (81) 0 3.0519E-1 V EGA Ion Pump High Voltage monitor

EGA_ION_PUMP_CUR (82) -4.2334 1.2386E-2 µA EGA Ion Pump Current monitor

EGA_SWEEP_VOLTAGE (83) 0 1.2208E-1 V EGA Sweep Voltage monitor



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EGA_MULTIPLIER_VOLT (80) 0 2.4416E-1 V EGA Channel Electron Multiplier high voltage monitor

EGA_EMISSION_CUR (72) 0 2.000E-1 µA EGA Ion Source Emission Current monitor NOTE 7

EGA_TRAP_CUR (71) 0 2.000E-1 µA EGA Ion Source Trap Current monitor NOTE 7

EGA_FILAMENT_CUR_1 (78) 0 3.0519E-4 A EGA Filament #1 drive current monitor

EGA_FILAMENT_CUR_2 (79) 0 3.0519E-4 A EGA Filament #2 drive current monitor

EGA_PLUS_5_VOLT (75) 0 4.2027E-4 V EGA CPU board +5V rail monitor

EGA_PLUS_12_VOLT (76) 0 1.2508E-3 V EGA Analog +12V rail monitor

EGA_MINUS_12_VOLT (77) 0 -8.9E-4 V EGA Analog -12V rail monitor

EGA_GEC_CUR (84) 0 3.0519E-4 A EGA Getter current monitor

Table 6: Voltage and Current Monitors

NOTE 4: This sensor has a significant sensitivity to both voltage and temperature. The initial coefficients get us to

+157/-99mA. Adding temperature compensation gets us to +75/-67mA:

result = result + 1.1108E-03 - 2.1072E-03 * TA_PWR_SPLY_2_TEMP (temperature in ºC)

Adding voltage compensation improves this to ±10mA:

result = result + 6.8538E-01 - 1.9355E-04 * RAW_TA_BUS_A_VOLT + 1.8425E-08 * RAW_TA_BUS_A_VOLT^2

- 5.7961E-13 * RAW_TA_BUS_A_VOLT^3 (note that this uses the raw ADC output for the bus A voltage)

NOTE 5: This sensor is sensitive to temperature. The initial coefficients get us to ±90mA. Applying temperature

compensation gets us to ±20mA:

result = result - 5.6695E-03 + 1.7142E-03 * TA_PWR_SPLY_2_TEMP (temperature in ºC)

NOTE 6: Initial coefficients get us to ±25mA. Temperature compensation improves this to ±10mA.

result = result + 1.2892E-03 - 4.0469E-04 * TA_PWR_SPLY_2_TEMP (temperature in ºC)

NOTE 7: Not valid after the filament short on SOL 4.

2.4 Status Channels There are several channels that are used to report digital status.

EGA_STATUS_BITS (70) This is a 16 bit status word that shows the internal status of the EGA.

Bit Function

0 Emission ON

1 Filament 1 selected

2 Filament 2 selected

3 High Voltage Enabled

4 CEM High Voltage Enabled

5 Sweep High Voltage Enabled

6 Currently Sweeping

7 Emission Current Setting (0 = low, 1 = high)

9,8 Emission Energy (NOTE 8)

00 -23V (0V)

01 -27V (-3V)

10 -37V (-13V)

11 -90V (-66V)

10 Emission Fault

11 Magnet Sensor 1 Fault

12 Magnet Sensor 2 Fault

13 - 15 Unused

Table 7: EGA Status Bits



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NOTE 8: The filament short on sol 4 altered the emission energy control circuit. After sol 4 the

emission energy was 24V less. The post-short values are in parentheses.

EGA_FILAMENT_1_SEL (73), EGA_FILAMENT_2_SEL (74) Prior to the filament short on Sol 4, these two channels provided positive feedback that the

intended filament was truly selected. The selected filament should read 3.3333V, and the other

filament should read 1.6666V. The filament short altered the circuit configuration such that these

readings are not meaningful after Sol 4.

EGA_AVG_IDLE_CALLS (88), EGA_MIN_IDLE_CALLS (89) These two channels track the load on the EGA CPU. The “Idle” function is called repeatedly

whenever the CPU is not busy. This function simply accumulates statistics on how often it is

called. The collected statistics are read out, and the accumulations reset every time an EGA

engineering packet is created.

EGA_AVG_IDLE_CALLS is the average number of times the idle function was called per second

since the last engineering packet. EGA_MIN_IDLE_CALLS is the minimum number of idle calls

in any second since the last engineering packet. Together, these channels give an indication of

both the average and the peak load on the CPU.

2.4 TA_MANIFOLD_PRES (0), TA_OUTLET_PRES (2)

There are two pressure sensors in the TEGA plumbing. The Manifold Pressure Sensor is

located in the plenum between the carrier and calibration valves and the TA inlet valves.

This sensor is used to regulate the gas flow through the ovens. The Outlet Pressure

Sensor monitors the pressure at the TA inlet to the EGA. Both sensors exhibit significant

nonlinearity at very low pressures, but become quite linear as the pressure increases (see

section 5). As a result, there are two equations for converting the raw value to pressure

for each sensor.

Channel Threshold A B C Constraint

TA_MANIFOLD_PRES raw < 3760 0.1613 -0.000134 2.83E-08

NOTE 9 raw ≥ 3760 -0.2557 8.35E-05 0

TA_OUTLET_PRES raw < 2865 1.123 -0.00084 1.56E-07

NOTE 10 raw ≥ 2865 -0.2182 8.02E-05 0

Pressure = A + B*raw_pressure + C*raw_pressure^2

Table 8: Pressure Calibration Parameters

NOTE 9: TA Manifold at +65. There were occasions where the manifold was not run at

+65C. See section 5 for temperature corrections.

NOTE 10: EGA Manifold at +35

2.5 Oven and Shield Error Signals

TA_OVEN_ERR (44), MEM_OVEN_ERR (57), TA_SHLD_ERR (45), and

MEM_SHLD_ERR (58)

The oven and shield control systems use a high-gain difference amplifier to subtract the

commanded temperature from the measured temperature. This difference is read out

every 3.3mS and used by the software to calculate the proper width for the next pulse.



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The exact conversion from the error signal to degrees is different for each TA and also

varies with the temperature, but a reasonable estimate is 631 dN / degree for the oven

error and 763 dN / degree for the shield error.

This measurement is reported two ways. The TA_OVEN_ERR and TA_SHLD_ERR

channels take an extra reading of these channels, while the MEM_OVEN_ERR and

MEM_SHLD_ERR report the last scheduled (3.3mS) reading.

2.6 TA_T_HEATER_TEMP (23)

The “T” heater is a heater / temperature sensor assembly on a plumbing junction between

each oven and the manifold. There is one “T” heater for each oven. The assembly

consists of a coil of heater wire wound on the plumbing junction wired in parallel with a

100Ω PRT. The PRT is mounted on the metal support for the junction. This assembly is

driven by a PWM controller that measures the parallel resistance in between the pulses to

determine the temperature.

As usual, there is a twist: The current source used to measure the resistance of the

assembly has a significant temperature coefficient.

Calculating the temperature requires several steps:

1) Calculate the sense current (IS) based on the smoothed

TA_PWR_CNTL_2_TEMP engineering channel

1000

L_2_TEMPTA_PWR_CNT102.17937506.9 -2 ××−=SI

2) Calculate the resistance of the assembly, RT.

S

TI

rawR

×

×−××=

−−

2117.19

103603.1108490.4 24

3) Use RT and the known resistance of the heater winding (RH) to calculate the

resistance of the PRT, RS.

TH

THS

RR

RRR

−

×=

4) Calculate the temperature of the PRT (TS) from RS using our standard PRT

equation 4

0

3

0

2

00

×+

×+

×+

×+=

R

RE

R

RD

R

RC

R

RBAT SSSS

S

Where R0 = 100,

A = -245.941,

B = 236.19,

C = 9.87813,

D = -0.300534, and

E = 0.176804

5) And finally, calculate the temperature of the actual plumbing (TT) from TS.

778.500156.1 +×= ST TT



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Table 9 gives the RH value for each of the cells.

Cell # RH

0 50.624

1 50.194

2 50.839

3 50.624

4 50.624

5 50.624

6 50.839

7 50.409 Table 9: “T” Heater Winding Resistances

2.7 Oven and Shield Voltage and Current

MEM_OVEN_VOLT (52), TA_OVEN_PLUS_15_VOLT (32)

MEM_OVEN_CUR (53), TA_OVEN_PLUS_15_CUR (40)

MEM_SHLD_VOLT (54), TA_SHIELD_PLUS_30_VOLT (33)

MEM_SHLD_CUR (55), TA_SHIELD_PLUS_30_CUR (41)

In order to accurately calculate the power going to the oven and shield, we need to

measure the voltage and current during the power pulse. Since the A/D converter takes

roughly 16µS to do a conversion, it would not be practical to measure all four of these

during a single pulse. Instead, the readings are taken in a round-robin fashion with one

reading taken on each pulse. The reading is taken approximately 5µS after the start of the

pulse to allow the pulse to reach full voltage and the readout circuits to stabilize. These

readings are not accurate until the pulse width is greater than about 8µS (pulse_width >

160). The “MEM_” channels report the most recent of these timed readings.

The “TA_” channels are read out at some random time with respect to the power pulse.

They should not be used.

The conversions for these channels are linear, with a linear temperature correction for the

TA_PWR_CNTL_2_TEMP sensor, which is located in the middle of the circuit with the

temperature sensitivity. Table 10 gives the conversion coefficients for these 4 channels.

Channel A B C Accuracy

MEM_OVEN_VOLT -1.27190E-02 1.09495E-03 -2.08298E-04 ± 1mV

MEM_OVEN_CUR -4.91240E-02 2.32655E-04 3.24271E-04 ± 4mA

MEM_SHLD_VOLT -9.72473E-02 2.18239E-03 0.00000E+00 ± 10mV

MEM_SHLD_CUR 3.90616E-02 2.46171E-04 -6.50331E-04 ± 7mA

Result = A + B * raw + C * TA_PWR_CNTL_2_TEMP (TA_PWR_CNTL_2_TEMP in ºC)

Table 10: Conversion coefficients for Oven and Shield Voltage and Current

2.8 Pulse Width Monitors

MEM_OVEN_WIDTH (60)

MEM_SHLD_WIDTH (61)

MEM_T_WIDTH (59)



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These channels report the width of the most recent pulse from the respective PWM

controller. The oven and shield controllers are 16 bits with a resolution of 50nS, and the

“T” heater controller is 10 bits with 1µS resolution.

While calorimetric calculations are possible using these channels, the preferred method is

to use the data in the DSC science data packets.

2.9 TA_FULL_DETECT (42), TA_FULL_DETECT_RAW (43)

The flow of soil into the oven is monitored by an optical sensor. As soil particles fall into

the oven, they modulate the light falling on a photodetector. The

TA_FULL_DETECT_RAW channel is used immediately before a soil loading operation

to get “light” and “dark” readings that are used to set the thresholds for soil detection.

There is no “calibration” per se for this channel, but lower values indicate brighter light.

The TA_FULL_DETECT channel is the output of an analog integrator that sums the light

to dark transitions on the detector.

During a soil loading operation, high time resolution readings are collected on these

channels. These readings are sent in the LED science data packets.



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3 Calculating the Calibration Curves for the Oven Pt Sense Winding

The coefficients used to convert the resistance of the oven and shield sense windings to

temperature were determined for TEGA-1 and carried over to TEGA-2 without any

further validation. Additionally, the room temperature resistance of the windings were

measured twice during TEGA-2 assembly, and those measurements came out slightly

different. The Callendar – van Dusen method is applied to the TEGA-2 flight data to

check the validity of the coefficients and to select which set of resistance measurements

lead to believable temperatures.

The Callendar – van Dusen method uses four calibration points to fully define the R vs T

curve for a given alloy of Pt. The calibration points are:

• R0 at T=0ºC

• R100 at T=100ºC

• RH at some TH >> 100ºC

• RL at some TL << 0ºC

The Callendar – van Dusen coefficients are

• 0

0100

100 R

RR

⋅

−=α (eq. 1)

•

−

⋅

−−

=

1001

100

0

0

HH

HH

TT

R

RRT

αδ (eq. 2)

• 3

0

0

1001

100

1001

100

−

−+

⋅

−−

=LL

LLLL

TT

TT

R

RRT δ

αβ (eq. 3)

Given only α, one can get a first order approximation of R for a given T with

( )TRRT ⋅+= α10 (eq. 4). Given α and δ, one can calculate RT very accurately for

temperatures ≥ 0ºC using

−−+=

1001

10000

TTTRRRT δα (eq. 5). To get an

accurate RT for temperatures below 0ºC we also need the β coefficient, and the equation

is

−−

−−+=

3

00100

1100100

1100

TTTTTRRRT βδα (eq. 6).



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By substituting 100

δαα

⋅+=A ,

2100

δα ⋅−=B , and

0100

00

4<

⋅−

≥

=forT

forT

C βα (eq. 7, 8, and 9),

we can rewrite eq. 6 in the more familiar form ( )[ ]100132

0 −+++= TCTBTATRRT .

These four data points are not available in the flight data. The data points that can be

teased from the flight data are:

• RR at T = room temperature, measured during assembly for each oven

• TR, a good measurement of room temperature

• RH at T=359ºC for each oven. This point is from the “mystery peak” in the high

temp day 2 data, which we believe is the Curie transition in the Ni oven body.

Since the Curie point for Ni is sometimes given in the literature as 357ºC and

sometimes as 361ºC, the average of the two is used for these calculations.

• α, the normalized slope of R vs T from 0 - 100ºC, is given as 0.00391 in the

California Fine Wire datasheet. This is the same α as in eq. 1 above.

Since room temperature is not far from 0ºC, eq. 1 can be used to calculate R0 from RR

and TR. Solving eq. 1 for R0 gives 1

0+⋅

=R

R

T

RR

α. For oven 4, this yields

Ω=+×

= 33.9038125.02.00391

37.220R . The value used for the TA4 R0 was 33.6811Ω.

Figure 3: Sol 25 Mystery Peak for TA4

Figure 3 shows the “mystery peak” in the high temp day 2 run for TA4 on sol 25. After

some discussion, the science team concluded that the Curie point is at the peak of the

transition. This peak is at R = 79.262Ω. Plugging this into eq. 2 yields

1.8110

100

3591

100

35900391.033.9038

33.9038262.79359

=

−

×

−−

=δ .

There are no good candidates for RL and TL, so we can not calculate β. However, since

there are no transitions of interest below 0ºC, this should not be an issue.

1.5x10-3

1.0

0.5

0.0

Oven D

uty

Cycle

9085807570656055

Oven Sense Resistance

Sol 25 "Mystery Peak"



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Plugging these values for α and δ into equations 7 and 8 gives:

3103.9808100

1.811000391.000391.0 −×=

×+=A and

7

2107.0812

100

1.811000391.0 −×−=×

−=B .

The numbers used during surface operations were A=3.9080x10-3

and B=-5.80190x10-7

.

Using the new A and B values to recalculate the temperatures for the TA4 run shows that

we were 10.4 degrees hotter at the top of the ramp (Figure 4).

Figure 4: Comparison of old and new conversions for TA4

Applying the same procedure to the rest of the surface runs yields the following:

3.1 TA0:

RR = 38.367 and TR = 24.57

Ω=+×

= 35.0042124.57.00391

38.3670R .

Figure 5: Sol 70 TA0 Mystery Peak. Peak at 81.6168 ohms

1000

800

600

400

200

0

Ove

n T

em

pera

ture

10x1039876

TEGA Time

old_TA_oven_temp new_TA_oven_temp

2.0x10-3

1.5

1.0

0.5

0.0

Oven D

uty

Cycle

90807060

Oven Sense Resistance

Sol 70 "Mystery Peak"



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From these numbers, we get 1.9822

100

3591

100

35900391.035.0042

35.00426168.81359

=

−

×

−−

=δ .

3.2 TA1:

RR = 39.092 and TR = 24.70

Ω=+×

= 35.6493124.70.00391

39.0920R (was 35.9247)


1.3416

100

3591

100

35900391.035.6493

35.6493951.83359

=

−

×

−−

=δ .

3.3 TA3:

RR = 38.481 and TR = 24.81

Ω=+×

= 35.0782124.81.00391

38.4810R (was 35.2055)


1.5

1.0

0.5

0.0

x1

0-3

9080706050

1.0

0.8

0.6

0.4

0.2

0.0

x1

0-3

90888684828078



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1.4126

100

3591

100

35900391.035.0782

35.078282.5156359

=

−

×

−−

=δ

3.4 TA5:

RR = 39.285 and TR = 25.02

Ω=+×

= 35.7848125.02.00391

39.2850R (was 35.6225)


1.8858

100

3591

100

35900391.035.7848

35.784883.5623359

=

−

×

−−

=δ

3.5 TA6:

RR = 38.625 and TR = 23.44

Ω=+×

= 35.3818123.44.00391

38.6250R (was 35.1898)


2.0

1.5

1.0

0.5

0.0

-0.5

x1

0-3

10090807060

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

x1

0-3

90807060



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2.1884

100

3591

100

35900391.035.3818

35.381882.2318359

=

−

×

−−

=δ

The δ values are summarized in Table 11, and shown graphically in Figure 10, along with

the average value.



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TA # δ

0 1.9822

1 1.3416

2 No data

3 1.4127

4 1.8110

5 1.8858

6 2.1884

7 No data

Table 11: Summary of δ Values

Figure 10: δ Values and Averages

This spread is also far too wide for these values to be useful, especially considering that

δ/1002 is the T

2 coefficient. Also, since δ describes a fundamental property of the Pt wire,

this is enough of a spread to warrant further examination.

As a quick check, the δ value for each TA was used to calculate a new temperature scale,

then each mystery peak was plotted against this new temperature scale.

Figure 11: Mystery peaks plotted each with its own temperature scale

2.2

2.0

1.8

1.6

1.4

δ

76543210

TA #

δ Mean δ = 1.77

2.0x10-3

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

Ove

n D

uty

Cycle

380370360350340330320310

Calculated Oven Temperature

Average δ Res_ov_duty_0 Res_ov_duty_1 Res_ov_duty_3 Res_ov_duty_4 Res_ov_duty_5 Res_ov_duty_6



CALIBRATION REPORT

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Figure 11 shows these results. The markers show the location chosen as the peak. Since

all of the markers lie exactly at 359°C, we can conclude that the δ values were calculated

correctly for the given input data. To see just how harmful this spread really is, the

temperature scale for each TA was recalculated using the average δ of 1.7703 for all of

the TAs. The results are shown in Figure 12. The markers now lie at 359.05 ± 4.45°C.

This isn’t great, but it isn’t horrible, either.

Figure 12: Mystery Peaks Using a Common δ of 1.77 and the earlier R0 measurements

But how bad is this spread at 1000°C? To get a rough idea, the TA4 max resistance was

converted to temperature using δ = 1.3416 and δ = 2.1884 (the two end members). This

yields max temperatures of 956.5°C and 1076.9°C, or 1016.7 ± 60.2 degrees. This is

really pretty horrible, but will have to do for this release of the RDR data.

3.6 Further Discussion

As it turns out, there were two measurements of the RR and TR taken for each oven: One

right after they finished cooling from the annealing bake, and a later one after the ovens

were integrated into the TA assemblies. The earlier measurement was probably more

accurate since it was done under very controlled conditions with a 6-digit, 4-wire

ohmmeter. Unfortunately, the derived R0 values do not agree between the two

measurements, and consequently, neither do the derived δ values. All of the above

calculations are based on the earlier measurement.

TA # First

measurement

Second

measurement

δ based on first

measurement

δ based on second

measurement

0 35.0042 35.2711 1.9822 2.4674

1 35.6493 35.9323 1.3416 1.8518

2 34.3812 34.4170

3 35.0782 35.1964 1.4127 1.6299

4 33.9038 33.6723 1.8110 1.369

5 35.7848 35.6133 1.8858 1.5763

2.0x10-3

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

Oven D

uty

Cycle

380370360350340330320310





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6 35.3818 35.1806 2.1884 1.8229

7 35.4578 35.2128 Table 12: Comparison of first and second oven measurements

Table 12 shows both sets of R0 and δ values. Using the later set of R0 measurements, the

spread in the δ values is somewhat larger than the spread using the later set (1.10 vs

0.85), and TA0 becomes a serious outlier. Leaving out TA0 and repeating the analysis of

the spread in temperatures using the mean δ value (in this case 1.65), shows the mystery

peaks at 359.4 ± 2.5 degrees (Figure 13). Calculating the spread at the max temperature

using the TA3 data and δ = 1.369 and δ = 1.8518 (the two end members ignoring TA0)

yields temperatures of 969.38°C and 1032.21°C, or 1000.8 ± 31.4 degrees. This is better

than the previous spread, but it leaves out poor TA0.

Figure 13: Mystery Peaks Using a Common δ of 1.65

This situation begs further analysis. Since δ is a fundamental property of the Pt wire, it

should be constant for all ovens. This analysis shows that there is some second-order

effect that we do not understand. One possibility is that Pt wire changes its resistance in

response to strain as well as temperature. Since each oven is built by hand, there could be

considerable variation in the tightness of the wind and the subsequent strain placed on the

wire by thermal expansion of the oven. Further analyses that could be done include

putting an oven and a bare loop of the Pt wire in a controlled environment to map out the

curve, but considering the variability we have seen it is not clear if one more data point

would help or hurt. If time and money permit, we will revisit this problem and release

updated RDR data.

2.0x10-3

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

Oven D

uty

Cycle

380370360350340330320310





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4 Converting TEGA DSC telemetry to true power

The TEGA PWM controller sends one power pulse to the oven and shield every

3.2768mS. For each pulse, TEGA reads out the voltage (V), current (I), and pulse width

(W). The power in the pulse is 65535

WIV ×× . These powers are then summed over some

number of pulses (N) for downlink to bring the data rate down to a reasonable value.

TEGA reads the voltage and current as 14-bit integers in arbitrary units. It does not

convert the voltage and current readings into true volts and amps prior to doing the

multiplication in order to save time in the DSC interrupt routine. It is the responsibility of

the ground data system to do this conversion after the fact. The true voltage is

11 DBV −× , and the true current is 22 DBI −× , where B1, B2, D1, and D2 are determined

during instrument characterization.

In order to calculate the true power in N pulses, we need the sum

( ) ( )

N

DBIDBVW

power

N

j

jj

j∑=

−××−××

=1

221165535

(Equation 1)

.

Since TEGA has no knowledge of B1, B2, D1, or D2, we need to develop a method where

those numbers can be applied on the ground. We can write Equation 1 as:

N

WDDIWDBVWDBIVWBB

power

N

j

j

N

j

jj

N

j

jj

N

j

jjj

×

+−−

=

∑∑∑∑====

65535

1

21

1

12

1

21

1

21

(Equation 2)

With this form, TEGA can calculate the 4 individual sums for downlink, and the gains

and offsets can be applied on the ground. These 4 sums are in the DSC telemetry packet

as “pulse” (∑=

N

j

jW1

), “power” (∑=

N

j

jjj IVW1

), “current” (∑=

N

j

jj IW1

), and “voltage” (∑=

N

j

jjVW1

).

These are assembled from the EDR data as follows:

• Pulse = ∑=

N

j

jW1

= OVEN_PULSE

• Power = ∑=

N

j

jjj IVW1

= OVEN_PWR_HI * 232

+ OVEN_PWR_LO

• Current = ∑=

N

j

jj IW1

= OVEN_CUR_HI * 232

+ OVEN_CUR_LO



CALIBRATION REPORT

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• Voltage = ∑=

N

j

jjVW1

= OVEN_VOLT_HI * 232

+ OVEN_VOLT_LO

• N = SUM_COUNT

From the instrument characterization we know that D1 and D2 are a dependent on the

temperature of the readout circuit, so we substitute

L_2_TEMPTA_PWR_CNT111 ×−−= CAD and

L_2_TEMPTA_PWR_CNT222 ×−−= CAD .

Table 13 lists the AN, BN, and CN coefficients for the flight unit. Note that these are the

same coefficients used to convert the MEM_OVEN_VOLT, MEM_OVEN_CUR,

MEM_SHLD_VOLT, and MEM_SHLD_CUR engineering channels. (See Table 10 in

TEGA Engineering Explained)

A1 B1 C1 A2 B2 C2

Oven -1.27190E-02 1.09495E-03 -2.08298E-04 -4.91240E-02 2.32655E-04 3.24271E-04

Shield -9.72473E-02 2.18239E-03 0 3.90616E-02 2.46171E-04 -6.50331E-04

Table 13: Oven and Shield Power Coefficients



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5 Pressure Transducer Calibration

Two pressure transducers are used to control and monitor the pressure and gas flow in

the TEGA instrument. One Sensor is mounted on the inlet side of the Thermal

Analyzer(TA) manifold and is used to provide feedback for the pressure regulation valves

from the two gas supply tanks. The second sensor is mounted in the Evolved Gas

Analyzer(EGA) manifold and is used to monitor the gas pressure adjacent to the Mass

Analyzer port and the pressure down-flow of the ovens. The transducer signals are

amplified and conditioned by electronics located in the Lower Payload Electronics bay to

give nominal signals in the pressure range from a few mB up to 1 Bar(14.7 PSI absolute).

The TA Manifold sensor is a 19C030A and the EGA sensor is a 19C015A transducer

both originally from the Honeywell(Sensym) and repackaged to provide a light weight

interface to the manifolds. Both transducers read pressure in the “absolute” sense in that

they can read pressures down to a vacuum.

Deficiencies recognized after the initial calibration required a recalibration done in-

situ on Mars to update the parameters used to transform raw counts to pressure and flow.

The Sol 4 Checkout along with EGA runs through Sol 66 are used to provide the

calibration constants used in the final processed data. Given an estimate for the absolute

pressure at the landing site, the Mass Spectrometer was used to locate several additional

points at higher pressures by using the initial Net Counts/mBar to extrapolate this

measurement to higher count rates at higher pressures. A fit for of the pressure as given

by the count rate in the Mass Analyzer on Sol 66 was then transferred to the Manifold

pressure transducer using data derived from the Sol 4 Checkout. The Sol 4 Checkout

consisted of several measurements made while both the manifolds were still capable of

being held at a static and equalized pressure by a diaphragm allowing the transfer of the

calibration from the TA_OUTLET_PRES to the TA_MANIFOLD_PRES. Later on Sol 4

a puncture mechanism breeched this diaphragm allowing flow to the Mass Analyzer

within the EGA and exhausting to Mars.

Cross checks for the converted pressure values was correlated against other information

related to the volume and flow characteristics of the TEGA plumbing system. These

checks demonstrated good agreement between calculated pressures and expected values

based on measured values of the Flight Model and equivalent runs in the Engineering

Qualification model.

The calibration values for the TA_OUTLET_PRES and TA_MANIFOLD_PRES are

two part fits shown in table 1 that convert the raw signal to a final pressure in Bar. A

second order polynomial is used below the indicated threshold and a linear fit above. The

equation for Manifold Pressure is valid for times when the TA_MANIFOLD_TEMP is at

or near +65 C and the Outlet Pressure conversion is valid when the

EGA_MANIFOLD_TEMP is at or near +35 C. An additional temperature compensation

equation is also shown in table 2 for the TA_MANIFOLD_PRES but is not applied in the

exported data. Although the devices are temperature compensated it was found that the

output signal is not correct when the device is changing temperature rapidly or has a

persistent thermal gradient across the transducer. The compensation provided can be



CALIBRATION REPORT

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applied only when the temperatures are stable and cannot be universally applied on a

point by point basis during or within a few minutes after abrupt temperature changes. No

temperature Compensation is available at the present time for the OUTLET Pressure

Sensor. The non-temperature compensated conversions are relevant to the majority of

the data taken during the mission.

Channel Threshold A B C Constraint

TA_MANIFOLD_PRES DN < 3760 0.1613 -0.000134 2.83E-08 Note 1

TA_MANIFOLD_PRES DN ≥ 3760 -0.2557 8.35E-05 Note 1

TA_OUTLET_PRES DN < 2865 1.123 -0.00084 1.56E-07 Note 2

TA_OUTLET_PRES DN ≥ 2865 -0.2182 8.02E-05 Note 2

Pressure=A+B*raw_pressure+C*raw_pressure^2 , C is zero if not shown

Table 1. Pressure Calibration Parameters

Note 1: TA Manifold at +65

Note 2: EGA Manifold at +35

Channel A B Constraint

TA_MANIFOLD_PRES - 0.0038 5.88E-05 Note 3,4

TA_MANIFOLD_PRES(Tarb)= TA_MANIFOLD_PRES+A+B*T

Table 2. Temperature Compensation for Manifold Sensor

Note 3: Manifold temperature stable and absolute manifold pressure less than 100mB

Note 4: Temperature in Celsius



CALIBRATION REPORT

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Figure 1. Example Conversion for the Manifold Pressure

The Pressure Transducers provided as part of the TEGA package are primarily to

control and monitor the gas flow through the system and as such are required to have an

absolute accuracy no better than 10% and a resolution on the order of a tenth of a mB.

The measurements made on Sol 66 used as the calibration basis have an estimate of

7.15mB for the ambient Mars atmosphere compared to a value of 7.85 mB from MET

reported post mission (about 4.5% error) under steady state conditions.

0.20

0.15

0.10

0.05

0.00

Estim

ate

d M

an

ifold

Pre

ssu

re ( B

ar)

5500500045004000350030002500

TA Manifold (RAW DN)

TA_OUTLET_PRES_SAM fit_TA_OUTLET_PRES_SAM_HT fit_TA_OUTLET_PRES_SAM_lin_HT

Sol 4 Checkout TA Manifold PressureHigh Temp

Coefficient values ± one standard deviationK0 =0.16128 ± 0.0226K1 =-0.00013386 ± 1.4e-005K2 =2.8325e-008 ± 2.13e-009Above 3760Coefficient values ± one standard deviation

a =-0.25568 ± 0.00193 b =8.3527e-005 ± 4.41e-007



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6 EGA Mass to Voltage Conversions

6.1 Theory

The Evolved gas Analyzer (EGA) is a magnetic sector mass spectrometer. Ions

generated in the ion source are accelerated by a sweep voltage, pass though a magnetic

field generated by a permanent magnet where they are deflected and arrive at one of the

four detectors. When a given mass is commanded to be scanned the instrument

automatically determines the correct sweep voltage to apply. This section outlines the

mass-to-voltage equations used in the instrument, the voltage-to-mass equations used in

the ground data reduction as well as the in-situ fine tuning of the calibration parameters.

The relationship between the mass-to-charge ratio, magnetic field strength, radius of

curvature to the detector, and accelerating voltage is expressed in VrBzm 2//22=

(Equation 3).

VrBzm 2//22= (Equation 3

1)

where:

r = radius of arc of ions deflected in the magnetic field

V = acceleration voltage applied to ions leaving the ion source (sweep

voltage)

B = magnetic field strength

zm / = mass to charge ratio of ion

For this instrument all ions are assumed to have a single charge )1( =z , making the mass

to charge ratio equal to mass mm =)1/( .

In order to get a specific mass to reach a detector the sweep voltage, V, is selected via a

16 bit DAC over a range of 2000 to 0 volts.

( )655362000⋅= dNV (Equation 4)

where:

V = Voltage

dN = 16 bit DAC code

Since the magnetic field strength B varies as a function of temperature it becomes

necessary to adjust the sweep voltage to compensate for the magnet temperature. During

surface operations the main magnet experienced temperatures from -50° to 0° C. Over

this range the function of the field strength versus temperature is mostly linear2.



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6.2 Practice

There are two modes in which the EGA can sample masses, sweep mode and hop mode.

In sweep mode the voltage is changed in steps in order to cover an entire mass range with

even sized steps in mass space. In hop mode only the center of peaks are sampled with

either 5 or 7 voltage settings evenly separated in mass space. (Figure 14)

Figure 14: Sweep modes vs. Hop modes

Sweep mode and hop mode have different requirements of the mass-to-voltage

calculations with regards to precision. Small errors in the conversion only affect the start

and end voltage for a sweep mode but can make a hop mode fall on the side of a peak or

completely miss the peak.

6.3 Calibration (coefficient derivation)

In order for hop modes to be precise it was necessary to understand the effect of the

magnet temperature on the location of peaks. To determine the exact coefficients for the

mass-to-voltage equations several masses on all four channels were continuously scanned

and tracked in voltage space while the EGA was slowly ramped in the Mars simulation

chamber from -50° to 20°C. Figure 15 shows an example of this data for mass 44 on

channel 4.



CALIBRATION REPORT

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Figure 15: Sweep voltage vs. magnet temperature for mass 44 on channel 4

For each channel the mass, voltage, and magnet temperature data was fit to an equation

with the form show in Equation 3 (see Figure 16). This equation is, in part, obtained

from equation 1 by setting the magnetic field strength B to a linear form )( hgxB += ,

combining constants, and solving for V. The linear part of equation 3 )( nmx + was

added to correctly fit the data although the m term was typically fixed to zero.

nmxM

cbxaxVxMf ++

++==

2

),( (Equation 3)

where:

V = Voltage in DAC steps (see equation 2)

x = Magnet temperature (average of the two raw magnet temperature

readings, see TEGA engineering explained)

M = Mass in AMU

a,b,c,m,n = Coefficients to be fit

Table 1 shows the actual results from these fits which were loaded into the EGA flight

software.

Channel 1 Channel 3

a -0.000257924 a -0.00827819

b 0.785900743 b 28.99002672

c 51848.86146 c 1042211.681

m 0 m 0

n 556.4766163 n 507.1783842

Channel 2 Channel 4

a -0.004017412 a -0.01473128

b 15.43483218 b 44.20884597

c 491018.0897 c 2069703.778

m 0 m 0



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N 534.7337957 n 612.561004

Table 1: EGA flight software default mass-to-voltage coefficients.

When the filaments in the ion source are run at high emission it is necessary to add 120 to

the n term from their nominal low emission values. This result was determined

experimentally by running the instrument at high and low emission and quantifying the

shift in peak location. Subsequently, if the instrument is well calibrated at high emission

is it necessary to remove 120 from the n term when switching to low emission.

Figure 16: Results from fitting channel 4 data to equation 3. Mass and magnet

temperature are displayed on the independent x and y axis, sweep voltage is on the

dependent z axis.

6.4 In-Situ Calibration

The mass-to-voltage equations described above provides an accurate (~ 1.0± AMU)

mass-to-voltage conversion over a large temperature range. There are however many

factors, such as filament warm up, that can effect the calibration in subtle ways. These

errors are significant enough that tightly clustered mass hop points would not be centered

on a peak simply using the default coefficients. To correct for this an in-situ calibration

was performed several times during each run.



CALIBRATION REPORT

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To fine tune the calibration, for each channel, two well known masses (M1, M2) with

large peaks are swept over with high resolution (Figure 17). The EGA flight software

then determines the center of those peaks in voltage space (V1, V2) and updates the

internal coefficients.

Figure 17: Actual calibration sweeps for channel 3 using masses 18 and 44. The dotted

black line shows where the instrument determined the peak centers to be.

Once the voltage at the center of two peaks has been found the instrument solves

equation 4 which is a simplified version of equation 3 where the magnet temperature

dependent terms have been replaced with A and B. Once solved the c and n coefficients

are update for each channel.

BM

AV

n

n += (Equation 4)

where:

(From Equation 3)



CALIBRATION REPORT

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VoltageV

MassM

nmxB

cbxaxA

=

=

+=

++= 2

x = Magnet temperature during the calibration sweeps

Using M1, M2, V1, V2 from the calibration scan solve equation 4 as a system of equations

using substitution.

( )( )

( ) ( )BMVMA

MM

VMVMB

⋅−⋅=

−

⋅−⋅=

111

21

2211

(Equation 5)

where:

M1=Mass of peak 1

M2=Mass of peak 2

V1=Voltage at center of peak 1

V2= Voltage at center of peak 2

Finally equation 6 describes how the c and n coefficients are updated after a successful

calibration.

Figure 18 shows the effect of a calibration scan on a tightly spaced hop sample on mass

44, channel 3. The black line shows where the peak center was calculated using equation

3 both before and after calibration. The green dots show where the hop points would

have been sampled.

( )( )mxBn

bxaxAc

−=

+−= 2

(Equation 6)



CALIBRATION REPORT

Version 1.20

4/22/2009

- 33 -

Figure 18: The effect of an in-situ calibration on a tightly spaced hop mode. The left side

shows where hop points (green) would have been placed using the default coefficients.

The right side is after the coefficients were updated with a calibration scan.

Before each calibration scan the instrument was typically commanded to reload the

default coefficient values. If a calibration scan fails for some reason (not enough counts,

could not find peak center) the default coefficients remained in place.

6.5 Ground Data Reduction

When processing data returned from the EGA it is necessary to invert the processes

described above. The EGA science data is in terms of counts at a certain voltage setting,

so converting from voltage to mass is required. Starting with equation 3 and solving for

M results in equation 7.

( )( )nmxV

cbxaxM

+−

++=

2

(Equation 7)

The calibration sweeps are also returned so adjustments to the coefficients over the

course of a run can be replicated on the ground.

6.6 References

Herbert, Christopher G., and Robert A.W. Johnstone. Mass Spectrometry Basics.

Florida: CRC Press, 2003

Wright, Wilfred, and Malcolm McCaig. Permanent Magnets. Great Brittan:

Oxford University Press, 1977

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