THERMOCOUPLE PLACEMENT
Proper thermocouple placement can eliminate many problems in the system. The probe should be placed so that it can detect any temperature change with minimal thermal lag. In a process that requires fairly constant heat output, the probe should be placed close to the heater. In processes where the heat demand is variable, the probe should be close to the work area. Some experimenting with probe location is often needed to find its optimum position.
In a bath process, addition of a stirrer will help to eliminate thermal lags. Since the thermocouple is basically a point measuring device, putting more than onethermocouple in parallel will provide an average temperaturereading and produce better results in air heated processes.
NOTE: If controls with "F" or "S" outputs drive loads with grounded or hot input terminals(not floating), an isolated thermocouple must be used. Otherwise, when bothinput and output are grounded, ground loop currents will result, causing errors and controller damage.
Standard thermocouple limits of error are 4°F or 0.75% of sensed temperature (half that for special) plus drift caused by improper protection or overtemperature. This is far greater than controller error, and can not be corrected at the sensor except by selection and replacement.
Before line voltage is applied,
Make sure the thermocouple type is correct, and properly connected (see section on thermocouples) to terminals 1 and 2 (red on2).
Make sure there is no AC or DC voltage leading or arcing to T/C.
Make sure the proper terminals are selected for line voltage. (8 & 9 for 12OV, 8 & 10 for 24OV)
Check to assure there are no heater shorts, or
shorts to ground, and no bare wires or frayed insulation.
Make sure correct
9
