PLC raises the temperature

A new compact temperature control expansion block has been released for Mitsubishi Electric's highly successful FX2N PLC range.

The new PID loop controller expansion block - the FX2N-2LC, has two independent control channels.

Each channel an be connected to all common (and some not so common!) thermocouple types such as K, J, R, S, E, T, B, N, PLII.

It is also able to accept resistance based temperature sensors such as Pt100 and jPt100.

Any FX2N PLC can have up to 8 of the new 2 loop controllers connected as expansion blocks.

Each FX2N-2LC will operate completely independently with its own PID loop control ability from the main PLC CPU.

All the PID loop algorithm and control processing is done in the block itself by its own processor.

The data from the block is then requested by the PLC via interrupts This prevents the main PLC sequence processor being slowed down by doing constant PID type calculations and control, as part of its normal programme scan.

To enable fast output processing the FX2N-2LC has two on board 24VDC digital output points.

These can be used for heating or cooling operations and are directly controlled by the blocks independent processor.

Having these loop outputs in the module creates extremely fast switching compared to normal PLC configurations, with internally controlled PID loops fed with temperature data from dedicated temperature input modules.

The FX2N-2LC also has 2 current detection (CT) inputs for use in heating applications.

These inputs allow the FX2N-2LC to check that the heating elements are actually active at any time.

The on board PID loop controller enables the execution of two position and PI control type processing.

The block comes complete with an optionally enabled auto-tuning facility.

This auto-tuning includes a bias set up function that compensates for any overshoots that may occur during auto-tuning configuration.

The temperature control block has an accuracy of up to +/-0.7% over the full input range with a sample rate of up to 0.5 seconds.

This new expansion block when combined with the data processing and programming instruction capability of the FX2N means that modular micro PLCs are no longer restricted to simple analogue control.

In fact they can surpass many larger PLCs in their PID loop control ability.

This cost effective combination has the added benefit of giving the user more system flexibility and greater communications options.

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