Assembly, Testing, and Calibration of the LaACES Sensor...

Assembly, Testing, and Calibration of the LaACES Sensor Interface A System for Measuring Atmospheric Pressure, Temperature, and Relative Humidity

into the Stratosphere

Jim Giammanco, Instructor of Physics

Louisiana State University Department of Physics and Astronomy

Baton Rouge LA June 2011

LaACES Sensor Assembly v12122011 of 33

WBEE Sensor Interface – Inventory of Parts Quantity Part ID Description Location

Semiconductors

2 CS1, CS101

LM234 (might be LM334) constant current source, TO‐92 3‐lead package

Black foam

1 D1

1N457A silicon small signal diode, axial leads

Black foam

1 D301

1N5819 Schottky diode, axial leads a 1N5818 may be supplied, it is functionally equivalent Black foam

2 D401, D402 1N4001 silicon rectifier diode, axial leads Black foam

1 PS1

ICS1230 pressure sensor DIP‐8 0.6" wide package

Black foam

2 Q401, Q402

2N3904 NPN Si transistor TO‐92

Black foam

2 U2, U101

AD820 single operational amplifier, DIP‐8

Black foam

2 U1, U201

AD822 dual operational amplifier, DIP‐8

Black foam

1 U301

REF‐02 precision 5.00 volt reference, DIP‐8

Black foam


Quantity Part ID Description Location

Other Electronics Black foam

1 F301

300 mA resettable fuse (for each of 2 battery packs) May look like either of these pictured.

Black foam

2 K401, K402

DPDT small signal relay DIP‐10, optionally 12V or 5 V coil

Black foam

1 D101, J101, and cable

1N457 diode pre‐prepared as temperature sensor, with ribbon cable leads and 2‐pin female header connector

Sensor Envelope

1 HS201, J201, and cable

HIH‐4000‐003 relative humidity sensor, pre‐prepared with ribbon cables

leads and 3‐pin female header connector IMPORTANT – The pressure sensor is packaged with a small slip of paper containing the manufacturer’s certification and test data. BE SURE TO RETAIN THIS ESSENTIAL INFORMATION

Sensor Envelope

5% Resistors These parts have 4 color bands to identify their value. The first three bands give the resistance and the fourth (GOLD) means 5% tolerance

1 R101 68 ohm 1/4 W 5% BLUE‐GRAY‐BLACK Resistor Envelope

1 R1 91 ohm 1/4 W 5% WHITE‐BROWN‐BLACK Resistor Envelope

1 R2 910 ohm 1/4 W 5% WHITE‐BROWN‐BROWN Resistor Envelope

1 R102 3.9K 1/4 W 5% ORANGE‐WHITE‐RED Resistor Envelope

2 R401, R402 2.7K 1/4 W 5% RED‐VIOLET‐RED Resistor Envelope

1 R202 6.8K 1/4 W 5% BLUE‐GRAY‐RED Resistor Envelope

2 R10, R203 10K 1/4 W 5% BROWN‐BLACK‐ORANGE Resistor Envelope

1 R104 20K 1/4 W 5% RED‐BLACK‐ORANGE Resistor Envelope

1 R205 75K 1/4 W 5% VIOLET‐GREEN‐ORANGE Resistor Envelope

1 R105 180K 1/4 W 5% BROWN‐GRAY‐YELLOW Resistor Envelope

Precision 0.1% Resistors Note that these resistors have more color bands than the 5% parts. The first 4 bands now give the resistance and the fifth indicates 0.1% tolerance

4 R6, R7, R8, R9 10K 1/4 W 0.1% BROWN‐BLACK‐BLACK‐RED Resistor Envelope



2 R4, R5 100K 1/4 W 0.1% BROWN‐BLACK‐BLACK‐ORANGE Resistor Envelope

1 R106

100K top adjust, 20‐turn potentiometer, or variable resistor 0.1" LS in‐line, Bourns 3299 marked "104" Resistor Envelope

3 R3, R201, R204 10K top adjust, 20‐turn potentiometer, 0.1" LS in‐line, Bourns 3299 marked "103"

Resistor Envelope

1 R103 1K top adjust, 20‐turn potentiometer, 0.1" LS in‐line, Bourns 3299 marked "102"

Resistor Envelope

Capacitors

17

C1‐C6, C101‐C103, C201‐C204, C301‐C302, C401‐C402

0.1 uF, 50 V, Kemet monolithic ceramic, 0.2" LS, marked "104" on one side. Ignore markings on the other side Capacitor Envelope

Hardware

1 PCB

Sensor Interface Printed circuit Board, LaACES/N5IB, 27‐APR‐2011, version 2.22

Loose

1 J1

2 pin power connector ‐ female

Hardware Envelope

1 J401

10 conductor IDC header – female. May be black or gray. Hardware Envelope

2 JP301, JP401

3 conductor vertical header ‐ male

Hardware Envelope

2 shunt/jumper

Shorting jumper for JP301 and JP401

Hardware Envelope

1 P1

2 pin power connector ‐ male

Hardware Envelope



1 P101

2 conductor right angle header – male (straight header may be supplied)

Hardware Envelope

1 P201


Hardware Envelope

1 P301

26 conductor (2x13) right angle header – male. May look like either of these pictured

Hardware Envelope

1 P401


Hardware Envelope

5 Socket

DIP‐8, 8‐pin, 0.3" spacing, machined pin IC socket

Hardware Envelope

1 Socket

DIP‐10, pin, 0.3" spacing, machined pin IC socket ‐ may be a cut down 14 pin socket, looks like the DIP‐8, or may be supplied as 2 strips of 5‐pin SIP sockets

Hardware Envelope

1 Socket

8‐pin 0.6" spacing, machined pin IC socket ‐ may be a 24‐pin socket that has been cut down to 8‐pin

Hardware Envelope

4 Standoff

Female‐female hex threaded aluminum standoff, #4‐40 x 1/4" Hardware Envelope

8 Standoff

Male‐female hex threaded aluminum standoff, #4‐40 x 7/8" Hardware Envelope


Building the WBEE Sensor Interface The WBEE Sensor Interface Subsystem will be constructed in stages. You will perform tests at the completion of each stage to verify correct assembly and function. Should a failure be detected at any stage of testing, that stage must be corrected before you can proceed with any subsequent assembly. It is good construction practice, and educationally valuable, to use a highlighter to mark off each component on the schematic diagram as you install them on the printed circuit board. You will gain more understanding of how the components fit together to make a working circuit. Power Supply and Voltage Reference Circuit Description Power for the Sensor Interface (and the BalloonSat controller) is provided by a 12 volt battery pack comprised of a pair of 2CR5 lithium photo batteries, each of 6 volts, and connected in series. The battery is protected from potentially damaging short-circuits by a resettable fuse. Though included here in Figure 1, the batteries and fuse (F301) are mounted external to the Sensor Interface and are connected by a 2-conductor cable and plug-in connector. A Schottky-barrier diode, D301 (1N5818) protects the system from damage should the battery be accidentally connected with reverse polarity. A portion of the Sensor Interface circuitry requires a precisely regulated reference voltage to ensure that measurements are stable and accurate. A precision, temperature compensated reference is included on the Sensor Interface board, provided by voltage reference integrated circuit U301 (REF-02). Alternatively, the reference may be supplied by the BalloonSat. A moveable jumper, JP301, selects the voltage reference source that is to be used. Power Supply and Voltage Reference Assembly You are about to solder a variety of electronic components onto a printed circuit board. Some components are unpolarized, meaning there is no preferred direction or orientation required. Resistors and common capacitors are examples of the unpolarized parts. For many other components, such as transistors, diodes, integrated circuits, and even sockets and connectors, the orientation is very

Figure 1. Power Source and Voltage Reference.


important. As you install individual parts, the instructions will remind you to check for proper orientation if required. If there is no reminder there is no need for a specific orientation. Just be sure to install the part in the right place. The printed circuit board has a printed outline of each part along with its part identification code to aid you in making correct placement. The printed outline will even help you get the correct orientation for polarized parts. Figure 2 shows the outline of diode D310. Notice the location of the banded end of D301 to the right. The actual part will have a silver band at one end. Just orient the part to match the outline. Install and solder the following components. Check off each component after you have installed and inspected its solder connections. Table 1. Power and Voltage Reference Order of Assembly

P1 2-pin power connector (at left in the photo). Before soldering P1, snap on its

mating socket, J1 (at right in photo), to maintain alignment of the pins during soldering. The shorter pins are inserted through the circuit board.

D301 Schottky barrier polarity protection diode, 1N5818, observe orientation of banded end. The band is silver. Be sure to match component outline. Form the leads to 0.4” spacing. Save the clipped leads to be used for test loops.

JP301 3-pin male vertical header connector, solder one pin only, then inspect to be sure the assembly is flush against the board and that the pins are vertical. If alignment is correct, solder the remaining two pins.

C301 0.1 microfarad (F) monolithic ceramic capacitor, marked “104”


U301 socket only

8-pin integrated circuit socket. Be sure the notch at one end of the socket is oriented to match the part outline on the printed circuit board

Test point loop 12V

Use some of the wire lead clipped from D301 to form a small U-shaped loop at the “12V’ label adjacent to D301. Use your needle-nosed pliers to form the loop. Insert both sides of the loop through the board and solder one lead, then re-align if needed before soldering the other lead. (Loop and locations shown by red arrows and inset in Figure 3)

Test point loop GND

Use some of the wire lead clipped from D301 to form a small U-shaped loop at the “GND” label adjacent to C301 (Shown by red arrow in Figure 3)

Test point Loop V-REF

Use some of the wire lead clipped from D301 to form a small U-shaped loop at the “V-REF’ label adjacent to JP-301 (Shown by red arrow in Figure 3)

Inspection and Testing Inspect your work. Look carefully for any unsoldered component leads, solder bridges between pads, or ugly looking solder joints. Fix any problems you may find before beginning resistance checks. Your team’s digital multimeter (DMM), in the ohmmeter mode, will be used to perform the following tests. Connect the positive (RED) and negative (BLACK) test leads of the multimeter as

Figure 2. D301 Orientation

Figure 3. Location of Test Loops


indicated in Table 2 below. Use jumper leads with alligator clips to make repeated connections more convenient. Fill in Table 2 with the resistance values actually measured by the multimeter. When an expected value is given as “greater than x” any value greater than the specified number, including the “OL” or “over-scale” indication of the DMM will satisfy the requirement. If the test is for “less than x” then any smaller value, including zero, is acceptable. If a specific numerical value is indicated as the expected result, your measurement may be as much as 50% high or low and should still be interpreted as meeting the criterion. Table 2. Power and Voltage Reference Resistance Checks

RED lead point BLACK lead point Expected Value Your Measured Value OK?

+ Pin of P1 Positive (unbanded) end of D301

Less than 5

+ Pin of P1 GND test loop Greater than 100K

+ Pin of P1 12 V test loop Less than 10K MOVE RED DMM LEAD TO “12 V” TEST LOOP

12 V test loop U301-2 that is, pin 2 of the socket for U301

Less than 5

12 V test loop CS1-1, the pin of CS1 nearest C3

Less than 5

12 V test loop U1-8 Less than 5


12 V test loop CS101-1, the pin of CS101 nearest R7

Less than 5



12 V test loop JP401-1, the pin of JP401 marked “12V”

Less than 5

MOVE RED DMM LEAD TO “GND” TEST LOOP

GND test loop U1-4 Less than 5




GND test loop PS1-2 Less than 5


GND test loop GND pin of P201 Less than 5

GND test loop GND pin of P101 Less than 5

In the tests above you verified that the +12 volt battery supply goes to all of the places where it is supposed to go, and perhaps even more importantly, that it is not going to places it shouldn’t. Did you mark “OK” for every test? If so, congratulations! You have successfully completed the first phase of construction. If any test did not pass muster, find and correct the problem before going on.


Pressure Measuring Circuit Description The circuit shown in Figure 4 provides a 0 - 3 V signal, representing an absolute pressure range of 0 to 1020 millibars (mb), to channel 0 of the BalloonSat Analog-to-Digital-Converter (ADC). Temperature compensation circuitry is included to preserve accuracy over a modest (-10 to +30 Celsius) range of operating temperatures. What follows is a fairly technical discussion of how the circuit works, and you can skip ahead to the assembly section if you wish. Or, seek out a friendly electrical engineer for assistance. The good news is that you can build this and make it work now, and learn how it works later. PS1, the ICS1230 (or the slightly less costly 1210) is an electromechanical hybrid device employing a piezoresistive strain gauge in a Wheatstone bridge configuration. Pressure changes applied to the internal strain gauge produce resistance changes that result in a differential output voltage of approximately 0 - 100 millivolts (mV). The transducer includes internal temperature compensation and a factory-trimmed gain setting resistor (Rint). The manufacturer recommends a constant current supply of approximately 1.5 milliamperes (mA) for operation within nominal specifications. CS1, the LM234 current source, operating from an

Figure 4. Pressure Measuring Circuit


unregulated +12 V battery supply provides the constant current drive. The network of R1, R2, and D2 compensates for temperature variations and helps maintain a constant bias current for the transducer. D1 is selected to be a diode whose temperature-voltage characteristics are a close match to the temperature response of the LM234. The output current is programmed by selection of R1 and R2. Details leading to the calculation below can be found in the LM124/234/334 series product datasheet. In this case the nearest 5% standard resistor values (91 and 910 ohms) have been selected. A dual FET-input operational amplifier (U1, AD822) forms a difference amplifier with a voltage amplification ratio of approximately 30 (can also be expressed as 30 db). It is important for circuit balance that R4 and R5 be closely matched, hence the choice of 0.1% tolerance precision resistors. The voltage gain is set by the ratio of the R4 (or R5) value to the equivalent resistance appearing between the inverting inputs of the two amplifier stages. Under normal operating conditions the manufacturer laser trims the value of RINT to provide an output voltage of 0 to 3.12 V over a pressure range of 0 to 15 psia (1034.2 mb) when R4 and R5 are 100 KΩ. If this is acceptable then R10 may be omitted (R10 = ∞) and R3 replaced by a shorting jumper (R3 = 0). If more precise control of the gain is desired then R3 and/or R10 may be required. The equation below gives the voltage gain of the difference amplifier in terms of the circuit resistances. Note that REFF is the parallel combination of RINT and R10, appearing in series with R3. If a gain smaller than about 30 is needed, R10 is omitted (R10 = ∞) and a variable resistor can be used at R3 to reduce the gain to the desired value. Should a voltage gain larger than 30 be required, chose a value of R10 that, with R3 =0, would yield a gain about 20% larger than the target, then use a variable resistor at R3 to bring the gain back down to the target value. The final amplifier stage (U2, AD820) is another FET input operational amplifier that forms a unity gain difference amplifier to provide an output voltage reference to ground suitable for the BalloonSat ADC. Again, for balance, it is essential that R6, R7, R8, and R9 be closely matched, so 0.1% tolerance parts are used once more.

1 2 1SET

0.134V 0.134 V89.3 and 10 893

1.5mAR R R

I

INT 10 4EFF 3 V 5 4

INT 10 EFF

and 2 andR R R

R R A R RR R R


Pressure Measuring Circuit Assembly Install and solder the following components. If you are so instructed, be careful to orient the components properly as shown on the component outlines on the printed circuit board. Check off each component after you have installed and inspected its solder connections. Use the supplied red plastic lead forming tool to bend the leads of resistors and diodes to the correct spacing. As shown in Figure 5, resistors should be formed with 0.5” spacing and diodes with 0.4” spacing. Several of the components will be illustrated the first time that type of component is encountered. Table 3. Pressure Measuring Circuit Order of Assembly

R1 91 ¼W 5% resistor (color code: WHITE-BROWN-BLACK) Form the leads of this and each following resistor to 0.5” spacing

R2 910 ¼W 5% resistor (WHITE-BROWN-BROWN)

R4

100K ¼W 0.1% precision resistor (BROWN-BLACK-BLACK-ORANGE-BROWN) Note that these precision resistors have an extra color band. Do not confuse them with the more common 5% resistors.

R5 100K ¼W 0.1% precision resistor (BROWN-BLACK-BLACK-ORANGE-BROWN)

R6

10K ¼W 0.1% precision resistor (BROWN-BLACK-BLACK-RED-BROWN)

R7 10K ¼W 0.1% precision resistor (BROWN-BLACK-BLACK-RED-BROWN)



R10 Do not install at this time – will be selected later, if needed






D1

1N457 or 1N457A silicon diode, observe orientation of banded end. The band is silver. Be sure to match component outline. Form the leads to 0.4” spacing

CS1

LM234 (might be LM334) constant current source, observe orientation of the flat and rounded sides of the component. Be sure to match component outline. Press the part down until it is about 1/8 to 1/4 inch above the board.

U1 socket only


Figure 5. Use of the lead forming tool for diodes and resistors


U2 socket only


PS1 socket only

8-pin wide-spacing integrated circuit socket. If there is a notch, be sure the notch at one end of the socket is oriented to match the part outline on the printed circuit board. If no notch is evident, either orientation is acceptable.

R3

10K 20-turn potentiometer, (variable resistor) marked “103” observe the location of the adjustment screw. Be sure to match component outline

Pressure Measuring Circuit Inspection and Testing Inspect your work. Look carefully for any unsoldered component leads, solder bridges between pads, or ugly looking solder joints. Fix any problems you may find before beginning resistance checks. Perform the resistance checks here in Table 4 for the pressure measuring portion of the circuit. Table 4. Pressure Measuring Circuit Resistance Checks


PS1-1 GND Test loop Greater than 100K

PS1-2 GND Test loop Less than 5



PS1-5 GND Test loop About 120K


U1-1 GND Test loop About 20K


U1-3 GND Test loop Greater than 100K

U1-4 GND Test loop Less than 5










Did you mark “OK” for every test? Your board should similar to Figure 6. If any test did not pass muster, find and correct the problem before going on to the temperature circuit.


Figure 6. Circuit board after completion of pressure circuit.


Temperature Measuring Circuit An ordinary PN junction diode can serve as an effective temperature sensor over a wide range of temperatures. The upper limit is around 400 kelvins, and the lower limit is well into the cryogenic range, down to a few tens of kelvins. When forward biased, the forward voltage drop exhibits a negative temperature coefficient of about -2.5 mV per kelvin. For example, at ambient room temperature (300 K) the forward voltage with about 1 mA bias current would be about 650 mV, rising to perhaps 900 mV at 200 K. The circuit shown in Figure 7 employs an FET input operational amplifier (U101, AD820) as a summing amplifier to provide adjustable voltage gain and DC offset trimming. An LM234 constant current source (CS101) maintains a steady bias current of about 1 mA through the sensor diode (D101, 1N457). Refer to the LM124/234/334 series product datasheet for details of the calculation of the current set resistor R101. This bias current will have a small temperature dependence of about +3 μA/K. In the usual payload design the current source is located inside the insulated payload enclosure and is not subject to extreme variations in temperature. But should tighter control of the bias current be desired, a compensating circuit such as that illustrated in the Figure 4 pressure sensor circuit may be employed.

101SET

0.0681V 0.0681V68

1mAR

I

Figure 7. Temperature Measuring Circuit.


Since the PN junction forward voltage will vary over a range of about 240 to 300 mV with the temperatures encountered in flight (-80 to +30 ºC, or about 200 to 300 K) a voltage gain of about 12 (22 db) will be needed. In addition, a DC offset will have to be subtracted so that the signal presented to the BalloonSat ADC is in the required range of 0 to 3 V with respect to ground. The gain, AV, of the amplifier is determined by For the values shown, the gain is adjustable between approximately 13 and 15, which has proved suitable for past payloads. Should more or less gain be required, adjust the resistor values as needed. Assembly of Temperature Measuring Circuit Install and solder the following components. If you are so instructed, be careful to orient the components properly as shown on the component outlines on the printed circuit board. Check off each component after you have installed and inspected its solder connections. Use the lead forming tool to bend the leads of resistors to the correct spacing. Resistors should be formed with 0.5” spacing. Table 5. Temperature Measuring Circuit Order of Assembly

R101 68 ¼W 5% resistor (BLUE-GRAY-BLACK)

R102 3.9K ¼W 5% resistor (ORANGE-WHITE-RED)

R104 20K ¼W 5% resistor (RED-BLACK-ORANGE)

R105 180K ¼W 5% resistor (BROWN-GRAY-YELLOW)




R103 1K 20-turn potentiometer, marked “102” observe the location of the adjustment screw. Be sure to match component outline


CS101

LM234 (might be LM334) constant current source, TO-92 package, observe orientation of the flat and rounded sides of the component. Be sure to match component outline. Press the part down until it is about 1/8 to 1/4 inch above the board.

U101 socket only


P101

2 pin right-angled male header connector. Be sure the plastic base is flush against the board and the pins are parallel to the board For some applications a straight, rather than right-angled, header may be supplied. If so, be sure the base is flush against the board and the pins are perpendicular to the board

105 106V

104

1R R

AR


Temperature Measuring Circuit, Inspection and Testing Inspect your work. Look carefully for any unsoldered component leads, solder bridges between pads, or ugly looking solder joints. Fix any problems you may find before beginning resistance checks. Perform the following resistance checks on the temperature measuring portion of the circuit Table 6. Temperature Measuring Circuit Resistance Checks







P101-2, marked “GND” GND Test loop Less than 5

Did you mark “OK” for every test? If any test did not pass muster, find and correct the problem before going on to the relative humidity circuit. Your board should now look like Figure 8.

Figure 8. Circuit board after completion of temperature circuit circuitcircuit


Relative Humidity Measuring Circuit The HIH-4000 relative humidity sensor utilizes a polymer plastic element that responds to changes in relative humidity by exhibiting a varying capacitance. Initial signal conditioning is integrated within the device in order to provide a temperature compensated linear output voltage in the range of 0.8 to 3.3 V for relative humidities ranging from 0% to about 75%. The output is ratiometric with respect to the supply voltage, so a well regulated 5 V supply is required. The REF-02 reference device described above and shown in Figure 1 provides a stable supply voltage. Only about 200 μA are required from the 5 V supply, well within the limits of the REF-02. The sensor needs a load resistance of not less than 80 KΩ, which is provided by R205. Over the measurable range of relative humidity the sensor output voltage span is greater than 3 V. Therefore the final signal conditioning circuit must attenuate (gain less than one) the signal slightly, as well as subtract a DC offset to present a 0 - 3 V signal to the BalloonSat ADC. Figure 9 shows an AD822 dual FET input operational amplifier (U201) operated as a summing amplifier with a voltage gain of approximately 2 (6 db) for the signal presented to its non-inverting input (pin 6). Voltage divider potentiometer R204 attenuates the output of the first amplifier stage before it is buffered by the second stage of U201, which is operated as a unity gain voltage follower. The amount of DC offset subtracted is controlled by voltage divider potentiometer R201. The voltage gain is somewhat dependent upon the setting of R201. Therefore the gain (R204) and offset (R201) adjustments interact with one another and must be adjusted alternately until the desired output span and base are achieved.

Figure 9. Relative Humidity Measuring Circuit


Assembly of Relative Humidity Measuring Circuit Install and solder the following components. If you are so instructed, be careful to orient the components properly as shown on the component outlines on the printed circuit board. Check off each component after you have installed and inspected its solder connections. Use the lead forming tool to bend the leads of resistors to the correct spacing. Resistors should be formed with 0.5” spacing. Table 7. Relative Humidity Measuring Circuit Order of Assembly

R202 6.8K ¼W 5% resistor (BLUE-GRAY-RED)

R203 10K ¼W 5% resistor (BROWN-BLACK-ORANGE)

R205 75K ¼W 5% resistor (VIOLET-GREEN-ORANGE)







U201 socket only


P201

3 pin right-angled male header connector. Be sure the plastic base is flush against the board and the pins are parallel to the board For some applications a straight, rather than right-angled, header may be supplied. If so, be sure the base is flush against the board and the pins are perpendicular to the board

P301 26 pin, 2 rows x 13 pins, right-angles male hader connector. May be either style pictured. Be sure the plastic base is flush against the board and the pins are parallel to the board

Inspection and Testing Inspect your work. Look carefully for any unsoldered component leads, solder bridges between pads, or ugly looking solder joints. Fix any problems you may find before beginning resistance checks. Perform the following resistance checks on the temperature measuring portion of the circuit Table 8. Relative Humidity Measuring Circuit Resistance Checks



U201-2 GND Test loop Same as U201-1








Did you mark “OK” for every test? If any test did not pass muster, find and correct the problem before going on to either the relay circuit (optional) or final assembly. At this stage of your work, your board should look like Figure 10.

Figure 10.Circuit board after completion of humidity circuit.


Relay Control Circuit (Optional Feature – not used for WBEE Payloads) Two identical double-pole, double-throw (DPDT) relays are provided to control peripherals that require a dry contact closure. The relays are activated by digital output bits from the BalloonSat. Driving an output bit HIGH turns on a transistor switch (either Q401 or Q402) and energizes the associated relay coil. Two diode-capacitor networks (C401, D401, C402, and D402) are transient suppression networks to prevent voltage spikes caused by abrupt switching of current through the relay coil inductances. A complete single-pole-double-throw (SPDT) group of contacts, as well as one normally-open (NO) contact from each relay, is brought out to a header for connection to external devices. Relays with either 5 V or 12 V coils may be used. A shorting jumper (shunt) is used at JP401 to select the source of relay coil voltage. If 5 V relays are to be employed, a +5 V supply must be connected via the ribbon cable connection to the BalloonSat. DO NOT use the REF-02 5 V output for relay drive, as the relays require more current than the REF-02 is specified to deliver.

Figure 11. Relay Control Circuit.


Assembly of Relay Control Circuit Install and solder the following components. If you are so instructed, be careful to orient the components properly as shown on the component outlines on the printed circuit board. Check off each component after you have installed and inspected its solder connections. Use the plastic lead forming tool supplied to bend the leads of resistors and diodes to the correct spacing. Resistors should be formed with 0.5” spacing and diodes with 0.4” spacing. Table 9. Relay Circuit Order of Assembly

R401 2.7 K ¼W 5% resistor (RED-VIOLET-RED)

R402 2.7 K ¼W 5% resistor (RED-VIOLET-RED)

D401 1N4001 silicon rectifier diode, observe orientation of banded end. The band is silver. Be sure to match component outline.

D402 1N4001 silicon rectifier diode, observe orientation of banded end. The band is silver. Be sure to match component outline.



Q401

2N3904 NPN bipolar transistor, observe orientation of the flat and rounded sides of the component. Be sure to match component outline. Press the part down until it is about 1/8 to 1/4 inch above the board.

Q402 2N3904 NPN bipolar transistor, observe orientation of the flat and rounded sides of the component. Be sure to match component outline. Press the part down until it is about 1/8 to 1/4 inch above the board.

K401 socket only

10 pin IC socket. May be a cut-down 14 pin socket. Be sure the notch at one end of the socket is oriented to match the part outline on the printed circuit board. May be supplied as 2 strips of 5–pin SIP sockets. Before soldering, snap a relay, or even a spare DIP socket onto the

SIPs to maintain the pin alignment, as pictured

K402 socket only

10 pin IC socket. May be a cut-down 14 pin socket. Be sure the notch at one end of the socket is oriented to match the part outline on the printed circuit board. May be supplied as 2 strips of 5–pin SIP sockets. Before soldering, snap a relay onto the SIPs to maintain the pin alignment, as pictured

P401

10 pin (2x5) right-angled male header connector. Be sure the plastic base is flush against the board and the pins are parallel to the board

JP401 3-pin male vertical header connector, solder one pin only, then inspect to be sure the assembly is flush against the board and that the pins are vertical. If alignment is correct, solder the remaining two pins.

Inspection and Testing Inspect your work. Look carefully for any unsoldered component leads, solder bridges between pads, or ugly looking solder joints.


Figure 12. Circuit board after completion of relay circuit.


Final Assembly and Testing During this next phase you will plug in the integrated circuit chips, apply power to the Sensor Interface and perform a series of tests and adjustments to verify that all of the measurement circuits are performing properly. When installing integrated circuits into their sockets, first be sure you have the correct part. Check the part identification code, here circled in Figure 13. Next, be very sure that the devices are inserted with the proper orientation. Most IC chips have a small notch at one end of the package (shown by the small arrow in Figure 13) that should be aligned with the notch on the socket and with the outline of the part on the printed circuit board. Often there is a small dimple in the package adjacent to pin 1. In addition, on the printed circuit board pin 1 of an IC is usually identifiable as the square (rather than round) copper pad on the printed circuit board shown by the long double arrows in Figure 13. Starting at the lower left, pins are numbered counter-clockwise around the package. Be sure that all the pins of an IC are fully seated into the socket. Occasionally it may be necessary to straighten the pins if they are not quite parallel. Gently pressing the IC against a flat surface with a rocking motion will gently bend the pins in a parallel configuration. Pressure Circuit Final Assembly and Testing The initial functional tests are performed with the sensor port open to the atmosphere. Your digital multimeter will be used in the DC Voltage measuring mode. Install the following integrated circuits into their respective sockets

PS1 ICS1230 Pressure Sensor. Note that pin 1, marked on the device with a tiny number and shown by the arrow in Figure 14, should be to the upper right corner, nearest C3.

U1 AD822 dual operational amplifier – shown in Figure 13. Do not confuse this with the AD820.

U2 AD820 single operational amplifier – do not confuse this with the AD822.

Connect a power supply (NOT turned ON yet) to power connector P1. Make sure – double check – that you have the right polarity. The positive voltage connection is the pin of P1

nearest P401. It is marked “+.” When you’re sure you have it right turn on the power. If you detect any smoke, funny smells, or odd noises, turn off the power right away.

Figure 14. Pin 1 of Pressure Sensor

Figure 13. Finding pin 1 and orienting the notch in an IC

pin 1 4

58


Connect the common (BLACK) lead of your DMM to the GND Test Loop, and set the DMM to read DC voltage on the 20 volt scale. Perform the voltage tests and fill in Table 10.. Table 10. Pressure Measuring Circuit Voltage Checks


PS1-4 GND Test loop Between 6 and 8 V

PS1-1 GND Test loop Between 2.5 and 4.5 V

PS1-3 GND Test loop Between 2.5 and 4.5 V, and about 0.1 V higher than PS1-1

U2-6 GND Test loop Adjustable to about 3 V using R3

If a vacuum pump is available, connect the tube from the pump to the pressure sensing port of PS1. Monitor the voltage at U2-6 and verify that the voltage decreases as the pressure applied to PS1 decreases. If a variable power supply is available, vary the power supply voltage from about 10 V to about 13 V and verify that the voltage at U2-6 doesn’t vary by more than a few millivolts. Turn off the power and disconnect the power wires from the board. If your pressure circuit passed all of these tests it should be working properly, and you can go on to test the temperature circuit. If any problems are uncovered, troubleshoot them first before continuing on to the temperature circuit.


Temperature Circuit Final Assembly and Testing Initial functional tests are performed with the sensor exposed to the atmosphere at room temperature. Install the following integrated circuits into their respective sockets U101 AD820 single operational amplifier U301 REF-02 precision 5 volt reference They are similar in appearance to the device that was shown in Figure 6. Connect the temperature sensor probe (supplied pre-built with a connector to match P101) being sure to observe the correct polarity of the probe. The positive lead of the probe is identified by a small embossed triangle on the plastic connector. This lead should plug onto the “TEMP” pin of P101. Place a shorting jumper onto JP301 (see Figure 15) such that the two pins nearest R201 (“INT” and “5V REF”) are connected together. This jumper selects the REF-02 on the Sensor Interface board as the source of the 5 V reference signal.

Apply power (+12 V DC) to power connector. Check your polarity once more. The positive voltage connection is the pin

of P1 nearest P401. It is marked “+” Connect the common (BLACK) lead of your DMM to the GND Test Loop, and set the DMM to read DC voltage on the 20 volt scale. Perform the following voltage tests. Table 11. Temperature Measuring Circuit Voltage Checks

BLACK Lead point RED Lead point Expected value Measured value OK?

GND Test Loop V-REF Test Loop 5.0 V

GND Test Loop U101-3 About 0.65 V

GND Test Loop U101-6 Adjustable to approximately 0.1 V using R103

GND Test Loop U101-6 Voltage decreases slightly when sensor is warmed between the fingers

GND Test Loop U101-6 Voltage can be increased/decreased by adjusting R106

Turn off the power and disconnect the power wires from the board. If your temperature circuit passed all of these tests it should be working properly, and you can go on to test the humidity circuit. If any problems are uncovered, troubleshoot them first before continuing on to the relative humidity circuit.

Figure 15. Selecting the reference voltage source.


Relative Humidity Circuit Final Assembly and Testing Initial functional tests are performed with the sensor exposed to the atmosphere at room temperature and ambient relative humidity. In an air-conditioned room it should be around 60%. The sensor is mildly light-sensitive and should not be exposed to bright light (direct sunlight or strong room light). Light exposure will not damage it, but will degrade the measurement precision. To protect the sensor from light exposure it has been fitted with a flexible shroud. . Install the following integrated circuit into its socket. U201 AD822 dual operational amplifier Connect the relative humidity sensor probe (supplied with a connector to match P201) being sure to observe the correct polarity of the probe. The positive lead of the probe is identified by a small embossed triangle on the plastic connector. This lead should plug onto the “+V” pin of P201.

Apply power (+12 V DC) to power connector P1. Check your polarity yet again. The positive voltage connection is the pin of P1 nearest P401. It is marked “+”

Connect the common (BLACK) lead of your DMM to the GND Test Loop, and set the DMM to read DC voltage on the 20 volt scale. Perform the following voltage tests. Table 12. Relative Humidity Measuring Circuit Voltage Checks

BLACK Lead point RED Lead point Expected value Measured value OK?

GND Test Loop P201-1, the pin of P201 nearest R102 marked “+V”

5.0 V

GND Test Loop U201-5 Between 1.5 and 3.5 volts

GND Test Loop U201-5 Voltage increases slightly when you exhale onto the sensor

GND Test Loop U201-1 Voltage can be increased/decreased by adjustments of either R201 and/or R204

Turn off the power and disconnect the power wires from the board. If your humidity circuit passed all of these tests it should be working properly, and you can go on to calibrating the sensors. If any problems are uncovered, troubleshoot them first before continuing.


Figure 16. Fully assembled board with all ICs installed in sockets and temperature and humidity sensors attached. Note that relays K401 and 402 have not been installed into their sockets, since they are not used in the WBEE payload.

Figure 17. Sensor Interface now mounted with BalloonSat controller, ready for mounting into flight enclosure.


Sensor Calibrations Accurate calibration of the pressure, temperature, and relative humidity sensors requires you to make a series of careful measurements using both your WBEE sensors and a known-accurate reference instrument. If time does not permit that process, it is possible to make an approximate calibration using manufacturer-supplied specifications and employing a special WBEE Sensor Test Set developed by the engineers at LSU. You will need the following resources and information in order to perform an approximate calibration: Working BalloonSat with calibration software loaded Laptop computer Digital Multimeter WBEE Sensor Test Set Working WBEE Sensor Interface circuit board Thermometer, or knowledge of the ambient room temperature Barometer, or knowledge of the current local barometric pressure Hygrometer, or knowledge of the current local relative humidity Manufacturer’s test data for your specific relative humidity sensor Connect your WBEE Sensor Board to your BalloonSat using the supplied 26-conductor ribbon cable. Connect the power cables to both the BalloonSat and the Sensor Board. Connect your laptop computer to the BalloonSat’s DB-9 serial interface port. Apply power to the BalloonSat / Sensor Board system. Start the Basic Stamp Editor and load and run the calibration software supplied by LSU. Calibration of the Pressure Sensor The National Oceanic and Atmospheric Administration (NOAA) launches two upper air sounding balloons each day from dozens of locations around the US. The data from these radiosondes are available online from several venues. When listening to the weather reports on television you may be exposed to a variety of units of measure in the reporting of weather data. The nominal measuring range of the ICS1230 pressure sensor on your WBEE Sensor Board is 0 – 15 psia (pounds per square inch, absolute pressure). This range corresponds, in various common meteorological units, to

0 – 1034.2 millibars (mb) 0 – 1034.3 hecto pascals (hPa) 0 – 757.2 millimeters of mercury (mm Hg) 0 – 30.54 inches of mercury (in Hg) Notice that the millibars and hecto pascals are actually numerically identical. NOAA reports radiosonde data using pressure units of hPa, altitudes in meters, and temperature in Celsius. In a typical balloon flight to 100,000 feet (30,480 m) your payload will encounter pressures as low as 10 mb, and temperatures as low as 75º C.


Reproduced below are a few selected lines of a NOAA upper air sounding

As you can tell from these data in Table 13, your pressure sensor will have to respond to pressures from about 1000 mb to about 10 mb. The sensor is factory trimmed to have 0 volts output at 0 mb, and the response is quite linear. Thus knowledge of a single pressure value and the corresponding sensor output can suffice to achieve an approximate calibration. The analog to digital converter (ADC) on your BalloonSat will convert the measured pressure to a binary number in the range of 0 to 255. The integer number produced by the ADC is referred to as the ADC counts. A value of 0 would correspond to 0 mb (perfect vacuum), and you can adjust your Sensor Interface Board give a user-selected ADC counts, up to 255 maximum, at a user selected maximum expected pressure. A typical calibration choice is to have ADC counts of 250 represent 1000 mb. You can use that criterion, along with knowledge of the actual ambient pressure at you location, to approximately calibrate your pressure measuring circuit. All you have to do is calculate the proper ADC counts that should be recorded for the actual pressure at your location at the time of calibration. The air pressure given in weather reports is usually the sea-level-adjusted pressure. The real pressure at your location may be less, depending on your altitude above sea level. For each 7.5 meters altitude, pressure diminishes by about 1 millibar. So be sure to ask your friendly meteorologist if the absolute or sea-level-adjusted pressure is being quoted.

72248 SHV Shreveport Reg Observations at 12Z 30 Sep 2010 ----------------------------------------------------------------------------- PRES HGHT TEMP DWPT RELH MIXR DRCT SKNT THTA THTE THTV hPa m C C % g/kg deg knot K K K ----------------------------------------------------------------------------- 1002.0 79 16.8 13.1 79 9.54 340 3 289.8 316.8 291.4 909.7 914 17.9 6.7 48 6.82 5 12 299.1 319.5 300.3 796.0 2045 14.8 -34.2 2 0.27 22 23 307.4 308.3 307.4 787.6 2134 14.7 -19.7 8 1.03 25 22 308.1 311.6 308.3 700.0 3123 11.4 -22.6 7 0.89 35 29 315.1 318.3 315.2 608.0 4278 1.4 -11.6 37 2.60 10 36 316.5 325.2 317.0 500.0 5830 -7.7 -19.7 38 1.61 350 38 323.6 329.3 323.9 400.0 7530 -18.3 -62.3 1 0.02 345 35 331.1 331.2 331.1 300.0 9610 -33.9 -72.9 1 0.01 340 48 337.5 337.5 337.5 200.0 12320 -53.7 -70.7 11 0.01 320 37 347.6 347.6 347.6 100.0 16570 -68.3 -78.3 23 0.01 350 6 395.5 395.6 395.5 50.0 20790 -61.3 -76.3 12 0.02 100 8 498.6 498.8 498.6 30.0 23960 -62.1 -78.1 10 0.03 95 11 574.8 575.0 574.8 20.0 26530 -54.1 -87.1 1 0.01 65 16 669.8 669.9 669.8 10.0 31040 -43.1 -79.1 1 0.08 125 15 857.5 858.5 857.6 7.0 33440 -44.3 -80.3 1 0.09 150 7 944.6 945.9 944.6

Table. 13. NOAA Sounding Data (abridged)


For example, Palestine TX is at an elevation of about 130 m. Suppose that the weather forecasters report the barometer (sea-level adjusted) currently stands at 29.97 in Hg. That converts to 1015 mb. Palestine’s 130 m elevation requires that you subtract about 17 mb, yielding 998 mb Use ratio-and-proportion to calculate the corresponding ADC count of 249. Simply adjust the GAIN trimmer on pressure circuit of your Sensor Interface Board until you calibration software is reporting 249 counts on the pressure channel (Channel 0). Calibration of the External Temperature Sensor To calibrate the temperature measuring circuit you will utilize the WBEE Sensor Test Set shown in Figure 18.. You will need a thermometer to measure the room temperature or have knowledge of the temperature by some other means. Determine the ambient temperature and record that value as TA Plug the temperature sensor into your Sensor Interface Board and use your digital multimeter to measure the voltage at U101-3. Record that value as VA. The 1N457 silicon diode used as the temperature sensor responds to temperature changes with a voltage that decreases linearly at the rate of about 0.0022 V for each 1 degree increase in temperature (a negative temperature coefficient). With that fact and your recorded VA and TA you can determine the equation (the equation of a straight line – slope and intercept) that relates diode voltage and temperature as shown here: Now use that equation to predict the diode voltage at the highest expected temperature during flight (say, +30º C) and at the lowest (say, 80º C).

ADCcounts 2501000mb

atmP mb

V80 A AC°

V30 A AC°

0.0022 80 C 0.0022

0.0022 30 C 0.0022

V V T

V V T

VA 0 0C°

V0 A AC°

T

VT A AC°

0.0022 solve for

0.0022

thus, at any temperature, T, the diode voltage will be

0.0022 C 0.0022

AV T V V

V V T

V

V T V T


Disconnect the temperature probe from your Sensor Board and instead connect the WBEE Sensor Test Set’s P101 to P101 on the Sensor Board using the 2-conductor cable supplied. You do not need to turn on the power on the Test Set yet. Move the switch SW3 to the LOW position while measuring the voltage at U101-3 on the Sensor Board. Adjust the TEMP LOW trimmer (R4) until that voltage is the same you calculated for the lowest expected temperature. Repeat the process with the switch in the HIGH position and adjust TEMP HIGH (R3) for the voltage calculated for the highest expected temperature. You have now prepared the Test Set to simulate the temperature probe for the remainder of the calibrations. Ordinarily you would like to set the temperature measuring circuit to produce ADC counts of about 250 at the lowest expected temperature, and counts of about 5 at the highest expected (note the inverse slope of this response). With the Sensor Test Set connected to the Sensor Interface Board, move the switch to the TEMP HIGH position and adjust the T-OFFSET trimmer on the Sensor Board (R103) until your calibration software reports ADC counts of 5. Move the switch to the TEMP-LOW position and adjust the T-GAIN trimmer (R106) until you see ADC counts of 250. These adjustments interact somewhat, so repeat them several times until no significant improvement is noted. Disconnect the Test Set and re-connect your temperature sensor. You should see ADC counts consistent with the ambient room temperature. Calibration of the Relative Humidity Sensor The manufacturer of the relative humidity sensor measures the characteristics of each sensor produced and supplies a document with the sensor reporting the results of those tests. Typically the sensor output at 0% and at about 75% relative humidity is tabulated. Locate the documentation that came packaged with your sensor. You will use those data to set up the WBEE Sensor Test Set to simulate the humidity sensor. Turn on the Test Set (it does not have to be connected to the Sensor Interface Board yet). An LED should light up indicating power is on and the battery is good. Use your DMM to measure the voltage between the TP1 test loop and the GND test loop, and adjust the RH-HIGH trimmer (R1) until that voltage is the same as the manufacturer reported for the approximately 75% relative humidity condition. Repeat the process to set the voltage at the TP2 test loop to the voltage reported for 0% humidity using the RH-LOW trimmer (R2). The Test Set is now set up to simulate your specific sensor. Connect the Test Set P201 to P201 on your Sensor Board using the cable supplied.

Figure 18. WBEE Test Set.


Move the humidity switch (SW2) on the Test Set to the LOW position and adjust the H-OFFSET trimmer on the Sensor Board (R201) until you see ADC counts of 5. Move the switch to the HIGH position and adjust the H-GAIN trimmer (R204) for ADC counts corresponding to the documented high humidity condition (about 189 counts). Again, these adjustments interact somewhat, so repeat them several times until no significant improvement is noticed. Calibration of the BalloonSat Internal Temperature Sensor The voltage reference integrated circuit (U5, AD780) on the BalloonSat incorporates a temperature sensor that may be used if you wish to monitor the temperature inside the paylo0ad enclosure during flight. To enable this feature you must place a shunt on jumper JMP3 that connected the middle pin to the TEMP pin. You will then adjust potentiometer RV1 to calibrate the sensor at romm ambient temperature. Determine the ambient temperature in the room and express it in kelvins as TA. Use the equation below to determine the ADC counts that should be output if the sensor is at TA. While running the calibration program on your BalloonSat, adjust RV1 until the calculated counts are displayed for ADC CH3. Your internal temperature sensor is now calibrated so that at temperature of 313 K (40° C) will produce ADC counts of 255, and each count will represent a temperature change of about 1.23 C°.

A

A

255 counts313K

for example: suppose = 23 C = 296 K

296K255 Counts 241counts

313K

TADC Counts

T

ADC Counts


Items for CSBF to pre‐install – sockets, connectors, and headers

Assembly, Testing, and Calibration of the LaACES Sensor...

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