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.