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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BINP CAPACITIVE AND ULTRASONIC HYDROSTATIC LEVEL
SENSORS A.G. Chupyra, G.A. Gusev, M.N.
Kondaurov, A.S. Medvedko, Sh.R.
SingatulinBINP, 630090, Novosibirsk, Russia
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• INTRODUCTION.
• MODIFICATIONS OF CAPACITIVE LEVEL SENSOR SAS,
  SASE.
• MODIFICATIONS OF ULTRASONIC LEVEL SENSORS ULS,
  ULSE.
• COMPARISION OF TWO KINDS OF THE SENSORS.
• CONCLUSION.
• REFERENCES.

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• Introduction
• Slow 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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• MODIFICATIONS OF CAPACITIVE LEVEL SENSOR SAS,
  SASE.

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 the second electrode of
capacitor, the capacitance of which is measured
in order 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 its
  internal parameters. To connect by turns Cr and
  Cz one can measure 3 periods T0,T1, T2 and
  calculate Cz removing parasitic capacitance C.

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• T0? 11 ?sec
• T2 gt 1118 ?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 030x10E-6 ?.
  
• Another feature of the capacitive sensor is
  level noise dependence from measuring level.
  Greater distance between free water surface and
  the electrode gt less capacitance and worse ratio
  signal/noise.

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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.

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
CgtF 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 IWAA4.
  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

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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.

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• Special transducers gt 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.

Sound field pictures of the typical piezoelectric
transducer
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• Near zone gt 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 lt d lt 2N
• This requirement determines the minimal distance
  from transducer to target surfaces.

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Unfocused immersion transducer parameters Table
1
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 a/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
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Time 0.2microsec/div Amplitude 0.2 V/div
Typical time response of V310-RU transducer
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The goal of the sensor electronics is to measure
time intervals with the accuracy as fine as
possible and to calculate the resulting values.
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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• Ultrasonic HLS prototype with Panametric
  transducer

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Ultrasonic HLS prototype with Krautkraemer
transducer
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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 dont 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 gt 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.
• Capacitive sensors are more inexpensive. For
  ultrasonic sensor price of transducer forms
  considerable part of costs.
• 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?! gt 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 gt 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 transducers 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 gt 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 gt more diagnostics and
  possibility of interfaces 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.p
  df ./
• 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/emb
  edded-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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• Thank you for attention!