| Level Controls & Alarms |
| Monday, 25 September 2006 |
Level Controls & Alarms - to maintain liquid nitrogen levels or process temperatures.
Model 10-32 Liquid Nitrogen Level Controller
The model 10-32 is a discrete-sensor unit giving fully automatic control of Liquid Nitrogen level in refrigerators, detector cryostats, traps etc. It may be operated from mains supplies of 230 or 115 volts, 50 Hz, or from 24 volts dc.
The four sensors provided are either mounted in a custom-built probe or on individual leads to allow positioning to suit different receivers.
The top and bottom sensors are used to detect high or low alarm conditions, the two control sensors define the limits of the normal control level zone.
Each sensor functions by detecting the marked difference in heat exchange characteristics between Liquid Nitrogen and cold gaseous Nitrogen, and triggers the appropriate channel of the detection circuit on being uncovered by the liquid.
An output socket to connect to a solenoid valve or Liquid Nitrogen pump is activated on the lower control sensor becoming uncovered, and remains active until the upper control sensor is covered.
The liquid level is thus maintained between the positions of the two control sensors.
Should the level fall below the low alarm sensor (eg. on failure of the liquid nitrogen supply) or rise above the high alarm sensor (eg. on solenoid valve failure) visual and audible warnings are actuated. Sockets are provided for the connection of remote alarm systems. In addition, the high alarm condition inhibits the "fill" condition and an additional socket, which may be connected to a back-up solenoid valve, is de-energised.
Fail-safe circuitry ensures that on disconnection or short-circuit of sensors, each channel of the controller goes to its safest condition -
ie. alarms are activated, control circuit goes to no output condition.
A "manual" button allows manual initiation of the filling cycle, before the level has fallen to its minimum control level.
A remote input socket allows the 10-32 to be triggered by a timer or programmer to operate at pre-determined intervals, whilst maintaining the continuous monitoring and control function. In addition, multiple units can be "cascaded" to fill simultaneously, so minimising supply line losses.
The 10-32 uses Platinum resistance sensors, which are free of drift and ageing problems, and allow sensor replacement without recalibration
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