AMI 186 Manual

MODEL 186 LIQUID LEVEL CONTROLLER
INSTALLATION, OPERATION, AND
MAINTENANCE INSTRUCTIONS
Rev. 3, Dec. 1996
PO Box 2509, 112 Flint Road, Oak Ridge, TN 37831-2509, Tel: [phone], Fax: [phone]
American Magnetics, Inc.
EXCELLENCE IN MAGNETICS AND CRYOGENICS

1
Introduction
The American Magnetics, Inc. (AMI) Model 186 Liquid Level Controller system is an
advanced, microprocessor-based solution designed to provide accurate and reliable
level monitoring and control of virtually any cryogenic liquid.
Capacitance-based level sensing
The system consists of a Model 186 Liquid Level Controller, sensor, connecting
cables, and an optional solenoid-operated fill valve. The instrument sensing element is
a 3/8 inch (9.5 mm) OD cylindrical capacitor constructed of stainless steel which
allows a cryogenic fluid to become the dielectric between the concentric plates. The
instrument measures the sensor capacitance which is directly related to the percentage
of the sensor immersed in the cryogenic liquid. The sensors are normally constructed
in overall lengths of up to 20 feet (6.1 m). The normal sensor maximum active length
is typically 7 inches less than the overall length.
Convenient display
The instrument is equipped with a 4-digit LED display which provides liquid level
indication in inches, centimeters, or percent as selected by a front panel switch. A
front panel switch allows the user to adjust the instrument length quickly and easily
for a specific active sensor length. The sensor active length can be entered in either
inches or centimeters. This length adjustment only effects the display and does not
change the calibration of the instrument.
Level control
The instrument has four level setpoints, two of which are control setpoints used to
control liquid level by the solenoid-operated fill valve. The other two set points are
alarm setpoints and can be set for other control or alarm functions. Output from this
second set of setpoints operates relay contacts in addition to the front panel LED
indications. All four setpoints are continuously adjustable from the front panel. The
automatic controller (fill) function can be manually overridden or disabled from the
front panel.
Remote computer monitoring or controlled operation
The Model 186 can be provided with an optional 0-10 volt DC signal on the rear panel
of the instrument for use with a recorder. A 4-20 mA current loop option is available
in lieu of the voltage signal. Computer interface options, including RS-232/422 Serial
Port/Data Logger or IEEE-488, are also available.

2
Introduction

3
Introduction
Front Panel Layout
1Fill indication LED 9MIN calibration push-button
2Activity LED 10 Approximate calibration push-button
3LED display 11 MAX calibration push-button
4HI level LED 12 Fill toggle switch
5A level LED (control band
upper limit)
13 Control mode rotary switch
6B level LED (control band
lower limit)
14 Raise/lower toggle switch
7LO level LED 15 Units mode toggle switch
8Power toggle switch
HI LEVEL
LO LEVEL
ACTIVITY
POWER
OFF
RAISE
LOWER
INCH
CM
%
MAX
~
MIN
CAL
HI
LO
LENGTH
SILENCE
Model 186
Liquid Level
Controller
AMI
AUTO
OFF
ON
FILL
A
B
INTERVAL
A
B}SET
POINTS
4
89 10 11 13 14 1512
57
6
23
1
100.0

4
Introduction
Rear Panel Layout
1Optional RS-232/422 or IEEE-488
communications port (RS-232
shown)
4Controller output receptacle
2Auxiliary DB-9 connector (see
Appendix for pinout)
5Power cord connector
3RG-59/U coaxial connector to
oscillator unit via the extension
cable
LINE VOLTAGE, 250 VA - 2A MAX
(RESISTIVE LOAD)
CONTROLLER OUTPUT
COMMUNICATIONS
50-60 Hz (SELECTOR SW. INSIDE)
J5
J2
AMERICAN MAGNETICS, INC.
OAK RIDGE, TN U.S.A.
INPUT POWER
RS-232
J8S11
ON
115 VAC 230 VAC
2 3 5
1
4

5
Introduction
Instrument/Sensor System Diagram
Model 186 instrument, control valve, and sensor system diagram.

6
Introduction
Specifications
Instrument Specifications
Input line voltage 115/230 or 100/200 VAC ±10%
Input line frequency 50-60 Hertz, 1 phase
Controller output 250 VA maximum @ 2A max current
(resistive load)
Readout accuracy 0.1%
Dimensions 3.8" H x 8.4" W x 11.1" D, Standard
3.475" H x 19" W x 11.1" D, Rack Mount
Weight 3.6 lbs. Standard; 4.3 lbs. Rack Mount
Operating
environment
15 - 50°C non-condensing
Analog Output Specifications @ 25°C
Integral non-linearity ± 0.012%
Resolution 16 bits
Total error ± 0.25% for 4-20 mA output
± 0.5% for 0-10 V output
Current drift (4-20 mA) 75 ppm/°C
Voltage drift (0-10 V) 100 ppm/°C

7
Table of Contents
1Installation............................................................................................9
2Calibration..........................................................................................13
Relationship between calibration and sensor length......................... 13
Calibration methods.......................................................................... 13
Variations in the dielectric with changing density ........................... 15
Open Dewar Calibration ................................................................................ 16
Closed Dewar Calibration.............................................................................. 16
Presetting the MAX/MIN calibration points .................................... 17
Closed dewar calibration procedure ................................................. 18
Approximate Calibration ............................................................................... 19
3Operation............................................................................................23
Sensor contamination........................................................................ 27
4RS-232 Communication/Data Logger Option.................................29
Serial port connector and cabling ..................................................... 29
Command/return termination characters .......................................... 29
Communication DIP Switch Settings ............................................................ 30
Baud rate control............................................................................... 30
Data logger output interval ............................................................... 30
Echo function.................................................................................... 31
Data logger function ......................................................................... 31
RS-232 Command Set Reference .................................................................. 32
Commands for controlling the units of measurement....................... 32
Commands for configuring permanent memory............................... 33
Commands for querying the configuration....................................... 34
Command for returning a level measurement .................................. 34
Error Codes .................................................................................................... 35
5IEEE-488 Communication Option ...................................................37
Command/return termination characters .......................................... 37
Communicating with the Model 186 ................................................ 37
Communication DIP Switch Settings ............................................................ 39
IEEE-488 primary bus address ......................................................... 39
IEEE-488 Command Set Reference .............................................................. 40
Device clear (DCL) command.......................................................... 40
Commands for controlling the units of measurement....................... 41
Commands for configuring permanent memory............................... 42
Commands for querying the configuration....................................... 43
Command for returning a level measurement .................................. 43

8
Table of Contents
Error Codes .................................................................................................... 44
Serial Poll Status Byte ................................................................................... 45
6Virtual Instrument Operation ..........................................................47
RS-232 Virtual Instrument............................................................................. 47
Launching and initializing the RS-232 VI........................................ 48
Interacting with the running VI ........................................................ 49
IEEE-488 Virtual Instrument......................................................................... 50
Launching and initializing the GPIB VI ........................................... 51
Interacting with the running VI ........................................................ 52
Running multiple GPIB devices ....................................................... 53
7Troubleshooting .................................................................................55
LED display not on ........................................................................................ 55
Erratic or erroneous level reading.................................................................. 56
Controller output does not energize............................................................... 57
Unit not responding to communications ........................................................ 57
WARRANTY ................................................................................................ 58
RETURN AUTHORIZATION...................................................................... 58
Appendix.............................................................................................59
4-20 mA current loop option.......................................................................... 59
Auxiliary connector J2 pinout........................................................................ 60
RS-232 cable DB-25 to DB-9 translation ...................................................... 61
Dielectric constants for common liquids ....................................................... 62
Index....................................................................................................63

9
1Installation
Warning
Before energizing the instrument, the earth ground of the power receptacle
must be verified to be at earth potential and able to carry the rated current of
the power circuit. Using extension cords should be avoided, however, if one
must be used, ensure the ground conductor is intact and capable of carrying
the rated current.
In the event that the ground path of the instrument becomes less than sufficient
to carry the rated current of the power circuit, the instrument should be
disconnected from power, labeled as unsafe, and removed from place of
operation.
Do not operate this instrument in the presence of flammable gases. Doing so
could result in a life-threatening explosion.
Do not modify this instrument in any way. If component replacement is
required, return the instrument to AMI facilities as described in the
Troubleshooting section of this manual.
1. Unpack the instrument
Carefully remove the instrument, sensor, oscillator and interconnecting coaxial cables
from the shipping carton and remove all packaging material. A rack mounting kit is
supplied if the instrument was purchased with the rack mount option.
Note
If there is any shipping damage, save all packing material and contact the
shipping representative to file a damage claim. Do not return the instrument
to AMI unless prior authorization has been received.
If the chassis is a table top model, place the instrument on a flat, secure surface.
Warning
Do not remove the cabinet feet and then reinsert the original screws. Doing so
could present a severe life-threatening electrical hazard. If removal of the
cabinet feet is desired, replace the original screws with screws not to exceed
1/4" in length.

10
Installation
Installing the sensor
2. Rack mount the instrument if desired
If the instrument has a rack mount chassis, follow the following procedure:
a. Attach the rack mount adapter pieces to the instrument by first removing
the four screws on the side of the instrument that attach the cover to the
chassis. Attach the rack mount adapter pieces to the sides of the
instrument by reinstalling the screws.
b. Install the monitor in a 19" rack by securing the front panel to the rail in
each of the four corners with mounting hardware supplied by the cabinet
manufacturer.
3. Install the sensor in the cryo-vessel
Exercise care when installing the sensor since dents, crimps, bends or other physical
distortions in the thin wall capacitor will change electrical characteristics possibly
causing calibration errors and/or disruption of proper instrument operation. Before
installing the sensor, the user may want to review the Calibration and Operation
sections to determine what, if any, calibration procedures may be necessary.
Note
The coaxial interconnecting cables and the oscillator are temperature
sensitive and should be mounted in such a manner as to avoid large
temperature changes such as those encountered in the path of dewar vents.
4. Connect the oscillator cable to the AMI sensor
Connect the oscillator to the sensor using a supplied 6 foot RG-59/U coaxial cable.
Ensure the oscillator is connected in the correct orientation (see page5 for a system
diagram). The cable length between the oscillator and the sensor should not exceed 6
feet.
Caution
Moisture or contaminants in any of the BNC coaxial connectors can short out
the sensor and cause a false ‘full’ level indication or other erroneous
readings. A pack of non-conductive electrical connection lubricant (ECL) has
been included with the liquid level sensor packaging to reduce the possibility
of this occurring. If desired, apply a small amount of ECL to any of the BNC
connectors that may be exposed to moisture. Mate the doped connectors then
remove any excess ECL from the outside of the connector. Added protection
can be achieved by covering the doped connections with a short section of
heat-shrink tubing.
Note: MSDS sheets for the ECL are available upon request.

11
Installation
Interconnects with oscillator and valve
5. Connect the instrument to the oscillator
Caution
Operation of the AMI Model 186 Liquid Level Instrument with a device other
than an AMI Liquid Level Sensor may void the instrument warranty.
Using the J5 coaxial connector, connect the instrument to the oscillator using a RG-
59/U coaxial cable. The length of the extension cable can be varied to suit the specific
application, however, varying the extension cable length has minor effects on the
calibration (varying this cable from 6' to 100' caused a 0.3% error when a 24" test
sensor was used). Calibration errors can be reduced or eliminated by calibrating the
instrument with the desired custom extension cable in place.
6. Install the optional solenoid-operated fill valve
Install the solenoid-operated fill valve by connecting the valve power cable to the AC
controller output receptacle on the rear panel of the instrument. The standard AMI
supplied valve has a 9/32 inch orifice and the input and output are tapped for 3/8 NPT.
Caution
When using a solenoid-operated control valve with the Model 186, ensure the
valve is configured for the operating voltage of the Model 186. Failure to do
so will result in faulty operation and may also result in valve damage.
7. Connect the instrument to the appropriate power receptacle
Warning
The Model 186 operates on 50-60 Hz power and may be configured for 115 or
230 VAC (100 or 200 VAC for Asian markets). The power requirements for
each instrument is marked on the calibration sticker on the bottom of the
instrument. Be sure your instrument is configured for your power source prior
to plugging in the line cord. Do not fail to connect the input ground terminal
securely to an external earth ground.
Ensure the front panel switch is in the OFF position. Verify that the instrument is
configured for the proper operating voltage by referring to the calibration sticker
affixed to the bottom of the instrument. If the operating voltage is correct, plug the
line cord into the appropriate power receptacle.
If the instrument operating voltage needs to be changed, ensure the instrument is de-
energized by disconnecting the power cord from the power source. Remove the
instrument cover and slide the voltage selector switch on the main printed circuit
board to the proper voltage. Replace the instrument cover.

12
Installation
Configuring power

13
2Calibration
Model 186 instruments are calibrated at the factory for a specific length sensor for use
in a specific liquid. The calibration length and calibration liquid are listed on the
calibration sticker on the bottom of the instrument. If the factory calibration method
utilized was approximate, the calibration length will be noted as an approximate
value.
Relationship between calibration and sensor length
The capacitance-based method of measuring the liquid level operates by measuring
the frequency of an oscillator, which is contained in the oscillator/transmitter unit. As
the liquid level varies, the value of the capacitance varies proportionally. Since the
dielectric properties of liquids vary and the component tolerances for the sensor and
oscillator introduce variations, a calibration is required to assure maximum accuracy
for a specific sensor immersed in the target liquid. The calibration MIN and MAX
settings correspond to the maximum and minimum oscillation frequencies,
respectively, for a given sensor and target liquid configuration.
The LENGTH setting of the instrument is only provided as a means of scaling the 0%
(MIN) to 100% (MAX) range of the measurement to meaningful units of length.
During the calibration it is important to accurately measure the distance between the
physical locations on the sensor corresponding to the MAX and MIN calibration
points. The measured value for the length will be used in configuring the instrument
for operation.
Calibration methods
The most straightforward calibration method is the Open Dewar Calibration which
requires the customer to have access to a filled dewar where the full active length of
the sensor can be dipped. The Closed Dewar Calibration method can be performed in
situations where it is not feasible for the customer to dip the sensor into an open
dewar, such as situations where the target liquid is under pressure. The closed dewar
calibration is more complex and may require initial preparations to insure success.
Occasionally customers ask AMI to calibrate an instrument and sensor for a liquid
which is not available at AMI for calibration purposes and/or for a sensor which is too
long to be calibrated at our facilities.
For the case of the target liquid being unavailable, AMI uses liquid nitrogen as the
reference liquid and an Approximate Calibration is performed using mathematical
manipulation of the ratio of the dielectric constants between liquid nitrogen and the
desired liquid. This procedure is outlined in the Approximate Calibration section
beginning on page19. The technique is intended to provide the instrument with an
approximate calibration so that it can be used immediately by the customer. However,
the customer is still expected to perform a more accurate calibration where feasible,
such as the open dewar or closed dewar calibration, with the target liquid.

14
Calibration
Calibration methods
For the case where a sensor is too long to be calibrated in AMI facilities, AMI will
perform a partial length open dewar calibration in liquid nitrogen, and then calculate
the MAX calibration point. A dielectric ratio may also be subsequently utilized to
adjust for a target liquid other than liquid nitrogen. The customer is expected to
perform a more accurate open dewar or closed dewar calibration if feasible.
As a quick guide for selection of the best calibration method available, a calibration
selection diagram is presented below. If the instrument and sensor are purchased as a
Figure 2-1. Calibration method selection diagram.
Instrument &
sensor purchased
together?
START
Verify sensor
specifications
Verify calibration
sticker on bottom of
instrument
Perform Open
Dewar Calibration
Is factory
calibration
correct?
Can Open
Dewar Calibration be
performed in target
liquid?
Can Closed
Dewar Calibration be
performed in target
liquid?
Perform Closed
Dewar Calibration
Perform
Approximate
Calibration
Go to Operation
Y
N
N
Y
N
Is factory
calibration
Approximate?
Y
Y**
N
** Factory Approximate Calibration should only be used if
open dewar or closed dewar calibration is not feasible in
the target liquid at the customer's facility.
N
Can Open
Dewar Calibration be
performed in target
liquid?
Can Closed
Dewar Calibration be
performed in target
liquid?
Y
Y
N
NY

15
Calibration
Calibration methods
unit from AMI, then the factory calibration will be adequate in most cases. However,
for the exceptions noted in the previous paragraphs (which are approximate
calibrations), the customer should perform a more accurate open dewar or closed
dewar calibration. A customer performed calibration is also required for sensors that
are purchased as a separate item from the instrument, since the instrument and sensor
were not both available for calibration at AMI facilities.
Variations in the dielectric with changing density
For cryogenic liquids the dielectric of the liquid will change with a change in density.
The amount of change is dependent on the properties of the specific liquid. Figure 2-2
illustrates the variations in dielectric for nitrogen vs. pressure under saturated
conditions.1Since the instrument uses a capacitance-based method for determining
liquid level, such a change in the dielectric of the liquid will result in a shift in the
level reading of the instrument. The calibration procedures described herein are most
accurate when applied in situations where the operating conditions of the cryo-vessel
are relatively constant, i.e. the operating pressure and temperature of the cryo-vessel
are relatively constant.
To minimize the effects of shifts in the dielectric of the target liquid, perform a closed
dewar calibration at the expected operating condition of the cryo-vessel. If this is not
feasible, then perform an open dewar calibration at atmospheric pressure and then use
the approximate calibration method to compensate for the shift of the dielectric when
1. Data obtained from NIST Standard Reference Database 12.
050 100 150 200 250 300 350 400 450 500
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5 Diel-1 (saturated liquid) Diel-1 (saturated vapor)
Pressure (psi)
Diel - 1
Figure 2-2. Dielectric vs. pressure for nitrogen under saturated conditions.

16
Calibration
Open Dewar Calibration
the cryogenic liquid is under pressure. For this type of approximate calibration, the
substitute reference liquid will be the target liquid at atmospheric pressure — see
page19 for a detailed discussion of the approximate calibration method. If any
questions exist in regard to calibration issues, contact AMI for assistance in
determining the optimal calibration strategy.
Open Dewar Calibration
The instrument should be energized with the sensor connected to the instrument via
the oscillator (see the system diagram on page5).
1. Slowly insert the sensor into the liquid until the level rests approximately one
inch below the top sensor hole and then press the MAX push-button through
the small hole provided on the instrument front panel. When the calibration
point has been accepted, the display will show "bbb.b" and the push-button
can then be released. The location of the liquid level on the sensor when the
MAX button is pressed becomes the 100% level. The 100% level should
always be lower than the upper hole to ensure the instrument will always
reach 100% in the event the overall sensor capacitance changes slightly due to
component drift, pressure variations, fluid impurities, etc.
2. Slowly withdraw the sensor out of the liquid to be measured until the level is
approximately even with the bottom hole in the sensor and then press the MIN
push-button through the small hole provided in the instrument front panel.
When the calibration point has been accepted, the display will show "bbb.b"
and the push-button can then be released. The location of the liquid level on
the sensor when the MIN button is pressed becomes the 0% level. This
completes the calibration procedure.
Note
Having a small amount of liquid on the sensor at the MIN calibration level
helps stabilize the sensor capacitance for 0% level indication.
3. Permanently install the sensor in the vessel and proceed to the Operation
section for directions for configuring the instrument.
Closed Dewar Calibration
A calibration can be performed in a closed dewar system by monitoring the liquid
level while transferring the target liquid to an initially empty (or near empty) dewar at
a constant rate. In order to insure success with the closed dewar technique, it is
necessary to prepare the instrument by presetting the calibration MIN and MAX
points outside the estimated level range. If the instrument is not prepared in this
manner before the calibration procedure, it is possible to reach the MAX calibration
point of the instrument before the target vessel is at the desired maximum level point.

17
Calibration
Closed Dewar Calibration
If minimum and maximum liquid level indication is available via some other means
(e.g. flow calculation, visual determination, point sensors, etc.), then the presetting of
the instrument is not necessary.
Presetting the MAX/MIN calibration points
The following procedure should be performed before installation of the sensor in the
target cryo-vessel.
1. Connect the extension and oscillator cables to the J5 coaxial connector on the
rear panel of the instrument (see page5 for a system diagram). Do not connect
the sensor. Energize the instrument. Press the MIN push-button through the
small hole provided on the instrument front panel. When the calibration point
has been accepted, the display will show "bbb.b" and the push-button can then
be released.
2. Connect the sensor to the oscillator cable (which is still connected to the
instrument via the extension cable). Press the MAX push-button through the
small hole provided on the instrument front panel. When the calibration point
has been accepted, the display will show "bbb.b" and the push-button can then
be released.
3. Calculate the factor Cadj using the following equation:
where Ltotal is the total sensor length in inches, Lactive is the active sensor length
in inches, and eis the dielectric constant of the target liquid.
4. Enter Cadj into the instrument by placing the front panel control mode rotary
switch in the SILENCE position. By using the RAISE/LOWER toggle switch
and holding it in the up or down position, adjust the displayed value up or
down. The display will move slowly at first and then faster. Once near the
desired value, simply release the switch momentarily and then resume
changing the factor at the slower speed. Once the desired number has been
reached, release the toggle switch.
5. Once the value for Cadj has been entered, momentarily press the CAL push-
button labeled as "~" (the tilde character) through the small hole provided in
the instrument front panel. When the value has been accepted, the display will
show "ddd.d" and the button can then be released.
6. With the sensor connected, again press the MIN push-button through the
small hole provided on the instrument front panel. When the calibration point
has been accepted, the display will show "bbb.b" and the push-button can then
be released. The presetting procedure is complete. Proceed to the closed
dewar calibration procedure.
Cadj120 1 2.1Lactive
5.2Ltotal
------------------------+ e1–
0.454
-------------
=

18
Calibration
Closed Dewar Calibration
Closed dewar calibration procedure
1. Install the sensor in the dewar and energize the instrument with the sensor
connected to the instrument via the oscillator and extension cables (see the
system diagram on page5).
2. Set the LENGTH to the active length of the sensor. After setting the
LENGTH, set the units mode toggle switch to the % setting. For details on
setting the LENGTH and units mode, refer to the Operation section of this
manual.
3. Connect a strip chart recorder to the recorder output terminals on the rear
panel of the instrument. If the recorder output is not available, the 4-20 mA
current loop output may be used if installed, or an installed communications
option can be used to query the instrument for the liquid level at regular time
intervals during the calibration procedure. If no remote monitoring or
communication option is installed, the level display must be manually plotted
vs. time during the procedure.
4. Commence filling the dewar. While the sensor is cooling down, there may be
a slow drift in the displayed liquid level. However, when the liquid actually
touches the bottom of the sensor, contact with the liquid surface may become
apparent by virtue of more random and frequent fluctuations in the displayed
liquid level. The liquid level trace will also start to show an increasing profile
with positive slope.
Once the indications of the contact between the sensor and liquid become
readily apparent, press the MIN push-button through the small hole provided
in the instrument front panel. When the calibration point has been accepted,
the display will show "bbb.b" and the push-button can then be released. This
point is the 0% level of the sensor.
Note
If the sensor is installed in the dewar with some small amount of liquid
already in contact with the sensor, then the final MIN calibration point can be
set before filling begins but after any thermally induced fluctuations in the
observed output have diminished. However, note that the active length of the
sensor is reduced by the initial level of liquid in contact with the sensor.
5. Continue the transfer while observing the liquid level trace on the strip chart
recorder or computer display, whose slope is proportional to the transfer rate.
The slope of the liquid level trace should decrease significantly when the
liquid reaches the hole in the top of the sensor.
When the break in the slope of the level trace occurs (i.e. the slope of the level
trace becomes 0 or horizontal), push the MAX push-button through the small
hole provided in the instrument front panel. When the calibration data has
been accepted, the display will show "bbb.b" and the push-button can then be

19
Calibration
Approximate Calibration
released. The level on the sensor when the MAX button is pressed becomes
the 100% level.
Note
If the instrument displayed a 100% reading before a break is observed in the
slope of the level trace, then the MAX calibration point set prior to the current
procedure has interfered. If this occurs, the customer has two options: 1) stop
the procedure, repeatedly enter a value of 120 for Cadj (see steps 4 and 5 of
the presetting procedure) until the current liquid level display falls below
100%, and then continue the procedure; or 2) continue the liquid transfer
until the liquid level is determined to be 100% by means other than feedback
from the instrument and then pressing the MAX calibration push-button.
6. To achieve a standard calibration of the sensor with the active region located
from the lower hole to one inch below the upper hole, use the level data from
the instrument to recalibrate the MAX point when the percent level
corresponds to one inch below the upper hole. Use the following equation to
determine the percent level at which to reset the MAX calibration point:
where Lactive is the active length of the sensor in inches. This technique can be
used assuming the sensor was built as a standard sensor. If the sensor was
made in a custom configuration, refer to the sensor documentation and/or
drawing or contact AMI.
Example: 20" active length sensor:
When the sensor is calibrated by the closed dewar procedure, the actual length
of calibration will be 21" (distance between the bottom and top holes in the
sensor). When the liquid is 1" below the upper hole, the display will show
95.2% [e.g. 100% −(1"/21" x 100%) ]. When the liquid level reaches this
point during usage, push the MAX calibrate button. The instrument and
sensor are now calibrated with a standard active region of 20". The LENGTH
setting of the instrument should also be configured for 20".
7. Proceed to the Operation section for directions for configuring the instrument.
Approximate Calibration
This procedure is the least accurate form of calibration and should be used only when
the aforementioned calibration procedures are not viable. The approximate calibration
method can be used in cases where the sensor cannot be dipped into the target liquid,
the full active length of the sensor cannot be dipped into an open dewar, or both.
Approximate calibration may also be useful for situations where the sensor cannot be
dipped into the target liquid under the expected operating pressure.
MAXpercent100 100 1
Lactive
----------------
–=