A.Chupyra IWAA10, DESY Hamburg, September 13-17, 2010 1 BINP CAPACITIVE AND ULTRASONIC HYDROSTATIC...

A.Chupyra IWAA10, DESY Hamburg, September 13-17, 2010

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BINP CAPACITIVE AND ULTRASONIC HYDROSTATIC LEVEL SENSORS

A.G. Chupyra, G.A. Gusev, M.N. Kondaurov, A.S. Medvedko, Sh.R. Singatulin

BINP, 630090, Novosibirsk, Russia

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1. INTRODUCTION.

2. MODIFICATIONS OF CAPACITIVE LEVEL SENSOR: SAS, SASE.

3. MODIFICATIONS OF ULTRASONIC LEVEL SENSORS: ULS, ULSE.

4. COMPARISION OF TWO KINDS OF THE SENSORS.

5. CONCLUSION.

6. REFERENCES.

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1. IntroductionSlow ground motion study for future accelerator projects and alignment of large accelerator machine components with high accuracy are important tasks now. One of the prevalent tools for solution of these tasks are Hydrostatic Level Sensors designed to work into the Hydrostatic Levelling System, which is based on principle of communicating vessels.

Since 2000 year BINP took part in development and fabrication of Hydrostatic Level Sensors in the network of team-work with FNAL and SLAC. For this time some modifications of capacitive and ultrasonic HLS sensors were developed.

During last 9 years more then 300 sensors of both type were fabricated and delivered to FNAL, SLAC, KEK and Montana Tech.

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The biggest delivery of BINP HLS sensors (138 capacitive and 49 ultrasonic) was made at 2008 to SLAC for LCLS project. The sensors were installed by SLAC team on the LCLS Undulator magnet line at the end of 2008.

Spring 2010:

12 SASE and 12 ULSE were delivered to FNAL for Montana Tech Laboratory,

10 SASE were delivered to KEK.

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2 MODIFICATIONS OF CAPACITIVE LEVEL SENSOR : SAS, SASE.

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BINP data acquisition module.Fogale HLS sensor at Aurora mine,

March 2000, Illinois.


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The task was to develop hydrostatic level sensor for slow ground motion study at different sites for NLC project. It was decided to develop capacitive HLS sensor.

Capacitive HLS sensor works on principal of capacitance-based sensing.The principal is to create a capacitor, the liquid surface being one electrode,the sensor electrode placed in air medium upper of water surface being thesecond electrode of capacitor, the capacitance of which is measured inorder to derive the distance between these two electrodes.

One of disadvantage of existing at that time Fogale HLS sensor was analog representation of output signal. It took to use long multiwire cables for data acquisition and power supply.

It was decided that electronics of the developed sensor had to have a built-in microcontroller to provide measurements, initial calculation of signals and interface for digital representation of the measuring data. The RS-485 interface was choose for the data acquisition system.


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A method used for the measurement is to convert variable capacitance into frequency, after that to convert the frequency to digital form. The developed circuit uses the idea presented at the work of N.Toth and Gerard C.M. Meijer [1]. General idea of the converter is an RC-generator with oscillating frequency determined by it’s internal parameters. To connect by turns Cr and Cz one can measure 3 periods T0,T1, T2 and calculate Cz removing parasitic capacitance C.

z

r

C

C

TT

TT

02

01

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• T0 11 sec

• T2 => 11÷18 sec (depending on water level in vessel).

• The time value of 214 periods is measured to determine the all periods.

• Measurement time for 3 periods is about 1 sec.

• Frequency of data acquisition is no more 2 Hz.

Because measured Cz is normalized with help of reference Cr the all drifts of last one directly influences on measured level value. Temperature coefficient for used Cr is 0±30x10E-6 . ℃Another feature of the capacitive sensor is level noise dependence from measuring level. Greater distance between free water surface and the electrode => less capacitance and worse ratio signal/noise.

z

r

C

C

TT

TT

02

01


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There is also nonlinear dependence of measuring level from capacitance. So each sensor needs in calibration. Linearization with 3-d order polynom is used.

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Test system from 4 prototype SAS sensors and 2 Fogale HLS sensors at BINP.

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SAS sensor at Sector 10, SLAC. SAS electrode


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•The capacitive Hydrostatic Level Sensor is a device with two independent parts:

•Upper part is with electronics;

•lower part, usually named as vessel, filled with the water.

Lower volume was designed in four modifications:

•a) Vessel-1 with separate outlets for connecting with air tubes and 12 mm water tubes: for the systems with “fully-filled” lower tubes.

•b) Vessel-2 with 2 outlets of 22 mm diameter for “half-filled” tubes.

•c) Vessel-3 with 2 outlets of 50 mm diameter for “half-filled” tubes.

•d) Vessel-4 with one outlet of 33,4 mm diameter for “half-filled” tubes.


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a) b)

c) d)


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The development of last modification of capacitive level sensor was initiated by SLAC for control system of LCLS Undulator magnet line.

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The electronics of SASE is mounted on two printed circuit boards. The board 1 includes Lantronix XPort [3], Power supply controller, DC-DC converter and transformer. The board 2 includes C=>F converter and flash microcontroller. The board 1 is at the right side, the board 2 is at the left one.


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3. MODIFICATIONS OF ULTRASONIC LEVEL SENSORS: ULS, ULSE.

The development of ultrasonic level sensor also was initiated by SLAC in 2004 for control of LCLS Undulator magnet line.A pulse-echo method is used in ultrasonic HLS for water level measurements.The ultrasonic hydro-location is well known and widely distributed method of distance measurements for many applications.

One of precise methods was described by Markus Schlösser and Andreas Herty

at their report presented at the 7th IWAA[4]. Their idea is to locate not only the

water surface in a vessel, but also two addition surfaces with calibrated distance

between them and at the calibrated distance to alignment reference target.

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Principle of organizing the

reference surfaces at the ULSE(from the M. Schlösser & A. Herty report)

H - distance from the water surface Hw

to external reference surface (point) Hp

12

112

RR

Rof

tt

ttDDH

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Some basic principles of ultrasonic sensor

• Pulse-echo method for water level measurements:

• Determine the location of free water surface in a vessel

• Determine the location of reference reflective surfaces

• Accurately measuring the time required for a short ultrasonic pulse, generated by a transducer to travel through a thickness of water, to reflect from the free water surface or from the reflective surface, and to be returned to the transducer.

• The result is expressed by the relation:

• d is the distance,

• v is the velocity of sound waves in water,

• t is the measured round-trip transit time.

2/tvd

04/19/23 A.Chupyra IWAA10, DESY Hamburg, September 13-17, 2010

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Special transducers => immersion transducers• These transducers are designed to operate in a liquid environment.

• They usually have an impedance matching layer that helps to radiate more sound energy into the water and to receive reflected one.

• Immersion transducers can be equipped within a planner or focused lens.

• A focused transducer can improve sensitivity and axial resolution by concentrating the sound energy to a smaller area.

• The sound that irradiated from a piezoelectric transducer does not originate from a point, but from all the surface of the piezoelectric element.

• Round transducers are often referred to as piston source transducers because the sound field resembles a mass in front of the transducer.

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For a piston transducer with:

• Diameter D,

• Central frequency f,• Sound velocity V.

Estimation of the near/far zone transition point N.

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Sound field pictures of the typical piezoelectric transducer

VDfN /)2/( 2


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Near zone => Far zone• The ultrasonic beam is more uniform in the far field zone

• The transition between these zones occurs at a distance

N "natural focus" of a flat (or unfocused) transducer.

• This near/far distance N is very significant: This area just beyond the near field where the sound wave have maximum strength.

• Optimal measurement results will be obtained when reflective surfaces are close to N area:

N < d < 2N

• This requirement determines the minimal distance from transducer to target surfaces.

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Parameter \ Transducer Type

Units V310-RU Panametric

H10 KB 3 Krautkraemer

H10 KB 3T General Electric (Krautkraemer )

Central frequency f MHz 5.0 10.0 7.0

Transducer diameter D mm 6.35 5.0 5.0

Beam spread angle α/2

Degree

(rad)

1.365

(0.0243 )

0.884

(0.0154)

1.263

(0.022)

near/far distance N mm 33.6 41.7 29.2

Unfocused immersion transducer parameters

Table 1

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Time: 0.2microsec/div

Amplitude: 0.2 V/div

Typical time response of V310-RU transducer

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12

112 tt

ttDDH of

The goal of the sensor electronics is to measure time intervals with the accuracy as fine as possible and to calculate the resulting values.

t1 t2 tof

Transmission ReceivingNext transmission

Time diagram of one measuring cycle

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Drawings of Krautkraemer and GE (former Krautkraemer) transducers.

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Typical characteristics of GE H10KB3T transducer.


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Real oscillograms of reflected signals.

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04/19/23 A. Medvedko 27

Ultrasonic HLS prototype with Panametric transducer

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Ultrasonic HLS prototype with Krautkraemer transducer

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04/19/23 A. Medvedko 29

Last mechanical design of ULSE.

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ULSE for Montana Teach.

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5. COMPARISION OF TWO KINDS OF THE SENSORS

Ultrasonic sensor has a lot of benefits in comparison with capacitive one:• more high absolute accuracy • more sensitivity at more high sample rate• measuring data don’t depend on electronics drifts (temperature and

time) because of calibration capability during each measuring cycle• no dependence of relation “signal/noise” from measuring level• high linearity of transfer coefficient (output signal => level)• no need in precise calibration – only accurate measurement of two

linear sizes for reference part

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Test of the ULSE and SASE sensors: green line – ULSE level, blue line – SASE level, purple line – level difference.

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Noise test of the sensors: green line – ULSE level, blue line – SASE level, purple line – level difference.

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Capacitive level sensors have now only two benefits.

1. Capacitive sensors are more inexpensive. For ultrasonic sensor price of transducer forms considerable part of costs.

2. Capacitive sensors are working during many years. There is a big experience of work with them. Ultrasonic level sensors have not such experience.

So very important question! “What is reliability of the ultrasonic transducers? How long they can work without essential worsening of their characteristics?!” => about half of used transdusers of H10KB3 type have failed since end of 2008!New modifications of the transducers with more protected place of cover soldering will be tested.

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CONCLUSION

The future behind Ultrasonic hydrostatic level sensors:

• Operating experience will grow => about 140 sensors were installed at Desy, more 30 at SLAC, 3 at FNAL and 12 will be installed at South Dacota.

• The technology of the transducer’s fabrication will be improved• The cost in process of growth of manufacture probably will be decreased

Next plans:• Fabrication of the ultrasonic sensors with last modification of the

Krautkraemer transducers for long test measurement => order for the transducers is under progress

• Upgrade of the sensor electronics for increasing sensitivity at least twice and for improvement of convenience of work => more diagnostics and possibility of interface’s choice by user (Power over Ethernet, RS-485, Canbus).

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6. REFERENCES

[1] Ferry N. Toth and Gerard C.M. Meijer “A Low-Cost, Smart Capacitive Position Sensor”, / http://ieeexplore.ieee.org/iel1/19/5183/00199446.pdf ./

[2] A. Chupyra, M. Kondaurov, A. Medvedko, S. Singatulin, E. Shubin “SAS family of hydrostatic level and tilt sensors for slow ground motion stadies and precise alignment” Proceeding of 8th IWAA04, Geneve, 2004.

[3]http://www.lantronix.com/device-networking/embedded-device-servers/xport.html

[4] M. Shlösser, A. Herty, “High precision accelerator alignment of large linear colliders – vertical alignment”. Proceedings of the 7th IWAA, Spring-8, 2002.

[5] A. Chupyra, G. Gusev, M. Kondaurov, A. Medvedko, Sh. Singatulin “The ultrasonic level sensors for precise alignment of particle accelerators and storage rings” Proceeding of 9th IWAA06, SLAC, 2006.

[6] A. Chupyra, G. Gusev, M. Kondaurov, A. Medvedko, Sh. Singatulin “The ultrasonic level sensors for precise alignment of particle accelerators and storage rings” Proceeding of 10th IWAA08, KEK, 2008.

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http://duteela.et.tudelft.nl/ferry/ieee.htm

http://www.lantronix.com/

http://www.lantronix.com/


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Thank you for attention!

A.Chupyra IWAA10, DESY Hamburg, September 13-17, 2010 1 BINP CAPACITIVE AND ULTRASONIC HYDROSTATIC...

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