The Model 135 is an advanced liquid helium level monitor which incorporates AMI's patented
sample-and-hold design with automatic helium level sensor vacuum burnout protection. The Model 135
is ideal for operation in systems where it is important to monitor the liquid helium level while
also minimizing the helium losses. Microprocessor-based electronics provide 0.1% readout accuracy.
Nonvolatile, read only memory maintains instrument calibration without battery backup. Watchdog timer
circuitry and low line voltage (brownout) detector prevent microprocessor lock-up and provide fail-safe operation.
The Model 135 adds "High" and "Low" alarm setpoints which activate front panel
LED warning indicators and rear panel relay outputs in the event of an overfill or liquid loss
condition. The alarms also energize an audible warning which can be silenced from the front panel.
"High" and "Low" setpoints are programmable from 0 to 100 percent
of sensor active length.
In order to minimize liquid helium loss, the Model 135 automatically energizes the
liquid helium level sensor
at user programmable time intervals and monitors the normal (resistive) zone as it progresses
from the top of the sensor toward the liquid surface. As soon as the normal zone reaches the
liquid surface, the level reading is saved and the current in the sensor is turned off until
the next sample interval occurs. An LED sensor current indicator is illuminated during each
sample. Sample intervals are user programmable from the front panel and can be set
between "0.0" (continuous reading) to "600.0" minutes or hours.
A manual update switch provided on the front panel can also be set to obtain continuous readings
during a helium transfer period or to manually force an immediate measurement.
The Model 135 provides automatic helium level sensor vacuum burnout protection.
A liquid helium level sensor energized in a vacuum environment will self-heat to the point of burnout
within seconds. AMI’s innovative microprocessor-based circuitry detects incipient sensor burnout
and de-energizes the sensor before damage can occur. A 5% increase in sensor resistance will trigger
this protection, causing the current to be switched off for 6 seconds before attempting to resume
normal operation.
The Model 135 is equipped with a 4 digit LED digital display which provides liquid helium level
indication in inches, centimeters, or percent as selected by a front panel switch. Front panel
sensor calibration allows the user to calibrate the instrument quickly and easily for any length
sensor. Calibration can be performed in either inches or centimeters of sensor active length with
automatic reading crossover between inches, centimeters, and percent.
The Model 135 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 Serial Port/Data Logger or IEEE-488, are also available.
View the Model 135 Manual
(Technical Support page)