Panel-Mount PID Temperature Controller

A panel-mount PID temperature controller reads a temperature sensor, compares the reading against a setpoint and drives a heating or cooling output to close the gap. It is the instrument that holds a process at temperature, which is why it appears on extruders, injection moulding machines, packaging lines, ovens, baths and environmental chambers rather than only on test benches.

The controllers on this page cover four panel sizes from 48×48 to 96×96 mm. Inputs cover ten thermocouple and RTD types plus 4-20 mA and 0-10 V, selected in the instrument menu rather than fixed at order. Outputs cover relay contacts, SSR drive, a PID current or voltage output and a linear transmit output, and some of those combine where the panel size allows.

The configuration is ordered as a code built from five positions. The size code sets the panel cut-out, the output code sets the switching form, the alarm code sets one or two alarm channels, and a trailing letter adds RS-485. Because the output position is one digit on some options and two on others, the code length changes with the configuration.

How a PID temperature controller works

The controller runs a control loop rather than a thermostat. A relay-only controller switches the heater fully on until the setpoint is reached and then fully off, which overshoots and then undershoots around the setpoint. A PID loop measures how far the process is from the setpoint, how long it has been away from it, and how fast it is moving, and adjusts the output proportionally rather than in steps. On the same heater, the PID loop settles closer to the setpoint and holds it there.

The output form decides how that adjustment reaches the load. A relay output can only switch, so the loop works by varying how long the relay stays closed within a cycle. An SSR drive switches solid-state, which allows the same proportioning at a much shorter cycle. A linear 4-20 mA or 0-10 V output drives a power controller or a valve rather than switching the load directly, and it is the form that suits a load too large for a contact.

Input type is a menu setting, not a hardware choice. A controller set for a type K thermocouple will read a plausible and wrong value from a PT100 on the same terminals, because the instrument is linearising the signal against the wrong curve. The input type is therefore part of the commissioning, not part of the order alone.

How to select the right controller

Start with the panel cut-out. It is usually already fixed by the enclosure, and on this series it also decides what is available: the 48×48 size carries either an SSR drive or a relay, not both, so a machine that needs a linear transmit output and a contact together cannot use that size.

Then settle the output from the load. A contactor or a solenoid valve suits a relay output. A solid-state relay or a thyristor unit suits an SSR drive, which switches faster and has no contact to wear. A power controller or a control valve suits a linear output, and a load that must also be recorded or fed to a plc suits a linear transmit output alongside the switching one.

Then the sensor and the alarms. Ten thermocouple and RTD types are covered, plus 4-20 mA and 0-10 V for a sensor that is already conditioned. Two alarm channels are available on the higher alarm code. Where the alarm is there to catch a failed heater rather than a high reading, the heater-break type is the one to specify, and it needs its two parameters set to suit the process before it can be relied on.

State the cut-out, the sensor type, the output form, the number of alarm channels and whether RS-485 is needed, and the code follows from those.

Limitations and points to confirm

This instrument is a controller, not a transmitter. It does not provide an isolated retransmission of the measured value unless the linear transmit output is ordered, and it does not record. A process that needs a documented temperature record needs a data logger or a recorder in addition.

The relay rating published here is a contact rating of 250 VAC at 3 A or 5 A, given as a single figure without being tied to a particular panel size or output code. A contact rating is not a load rating: an inductive load such as a solenoid or a motor draws a surge on break that a resistive load of the same nominal current does not, and the usual practice is to switch such a load through an interposing relay rather than directly from the controller.

Several figures that a specification often calls for are not in the supplied material at all, and they are listed on this page as information required rather than estimated: ingress protection, operating temperature and humidity, measurement accuracy, sampling period and dielectric strength. The alarm table in the supplied drawing also omits setting values 9 and 10, so those two are published as unknown.

Finally, the controller shown in the photograph carries a different reference from the series code given in the supplied document. Until that is resolved, treat the identification as open and quote the configuration you need rather than a code, so the two can be matched before the order is placed.