MercuryiTC
©2014 Oxford Instruments Omicron NanoScience. All rights reserved.
Page 144
14 THEORY OF CONTROL LOOPS
This chapter describes the general principles of the control loops used in the MercuryiTC.
14.1 General information on control loops
The iTC uses control loops to control the heater and optional gas valve.
• Temperature control of the heaters uses PID control.
• Temperature control of the gas valve uses a proprietary algorithm.
Control of temperature by varying the gas valve is slower than control by varying the heater
output. The iTC can be configured to operate using three possible automatic control methods:
• Automatic control of the gas valve with the heater output fixed.
This method provides a slow response to changes in temperature.
• Automatic control of the heater output.
This method provides a fast response to rapid falls in temperature, but a slow response to
rapid rises in temperature.
• Automatic control of both the gas valve and the heater output.
This usually provides the most stable control, as it can compensate quickly for rapid rises or
falls of temperature
14.2 General information on temperature control loops
A temperature control system consists of the following parts:
• A means of measuring the sample temperature (the temperature sensor).
• A variable source of heat (the heater).
• A control device to monitor the sample temperature and to control the output of the heater.
A temperature control loop is designed to maintain the temperature of the system as close as
possible to the setpoint. There are several factors that must be considered:
• The heat loss from the system, which may vary with time and temperature.
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