Introduction
Here we detail the use of a specific instruction that can be used to measure how long an input has been ON for.
Design Considerations
The TTMR instruction (available in FX2N, FX3U and FX3G PLCs), provides a method of measuring how long an input condition has been in the TRUE state to a minimum resolution of 100ms.
This will measure how long input X0 has been ON for and store this value in data register D0 as well as D1. The reason that 2 data registers are used, is explained as follows:
Data register D* contains the number of 100ms counts that the input condition has been in the TRUE state.
Data register D + 1* contains the number of 100ms counts that the input condition has been in the TRUE state, multiplied by a magnification factor as detailed below:
Therefore if the value from the example above in D0 is 7, but the magnification factor is K2 (rather than K0), then this means;
D0 = 7 = 700ms and
D1 = D0 x 100 = 70000ms or 70 seconds.
Further Information
For further information please refer to tthe FX PLC programming manuals.