In many systems, temperature not volume of liquid nitrogen, is the main concern. To maintain this constant temperature, a constant flow of liquid nitrogen is required.

The function of the temperature controller is to pass liquid nitrogen through the system, maintaining it at low temperatures. At the exhaust of this liquid nitrogen system, a temperature sensor is located. The temperature controller then increases or decreases the amount of liquid supplied to the system, on a basis proportional to the difference between the observed and expected operating temperatures.

This control is gained by the use of two valves, a simple on / off block valve and a control valve which limits the flow of liquid nitrogen.

The Temperature Control System
The control box incorporates a timer to switch the liquid flow temperature control system on and off as required. However, when the system is required more often, the liquid nitrogen flow can be reduced to a minimum and the system left ticking over.

The Control Box Face
The WEST 2073 is a self-tuning high performance microprocessor, with two gauges located on the front of the box. One gauge is the Regulated Supply, which sets the pneumatic pressure entering the I/P, the other gauge is the Pneumatic Signal, which is the pneumatic pressure from the I/P to the control valve. (An I/P is a unit which converts electrical current from the process controller to a proportional pressure in either filtered air or dry nitrogen gas.)

Options
The block valves fitted to the liquid nitrogen supply can be pneumatic or solenoid. If a pneumatic line is required, this can use either filtered air or dry nitrogen gas. If a voltage is required for a solenoid valve, then normally this will be either 24 VAC, 110 VAC or 240 VAC.

Equipment Codes
The variants on the Liquid Flow Temperature Control System are:

• Input Voltage
• Valve Type
• Output Voltage (if solenoid valve chosen)
• Air or Nitrogen gas (if pneumatic valve chosen)

The choices are:

• Input Voltages: 110 V, 240 V
• Valve Types: Asco 1/2" Solenoid, Asco 3/8" Solenoid, Worcester 1/2" Pneumatic and Actuator
• Output Voltage: 24 VAC, 110 VAC, 240 VAC

The equipment is thus specified:Input / Valve Type / Output, e.g. 240 V / 1/2" Solenoid / 100 VAC; being a temperature control system powered by 240 V with 1/2" Asco Solenoid Valve, and an Output Voltage of 100 VAC.