Dear all,

I have flowmeter that gives pulse every few milliseconds. The flowmeter pulses used to calculated the accumulated volume of the gas that passing through it in one hour. However, sometimes we have issue with the calculations and I'm thinking that we might missing pulses, I''m thinking (correct me if I'm worng) that the pulse comes while the plc is busy with execution the code. Then when it reads the input again for new cycle, it does not see the pulse because it is already passed (became low).

So, what would be the best practise to read the flowmeter pulse and don't miss any of them and to get accurate reading/volume?

The pulses wire is connected to digital input of 314C-2 PN/DP, this plc has multiple options regarding the input channels, I listed them in the screenshots. I don't have experience with these options.

regards

T_Ebrahem

jacek d

If an OB cycle which you use for counting is longer than pulse duration then you won't be able to count correctly because of the reason you gave.

With this CPU you have two options:

1. use HW interrupt to increase counter via code in HW interrupt OB;
2. use a hardware counter which, once properly configured, will do counting by itself.

This manual may be of help.

 Thanks, I read through the manual but still unclear to me. do you have example of the the first option? or maybe reference to a document. option 2, we don't want to add extra hardware.

qwazee

Using continuous high speed counting would be best. Have a look at the materials offered here: [Search: "31xC counting"]. These articles are centred around Step7 Classic but still applies for Step7 (TIA Portal).

Important: Do not work with REAL numbers. Work throughout with DINT when adding counting numbers to each other. Only the step where values are displayed to the user do you use REAL numbers to show the engineering unit.

These articles may also be of value: [Search: "totalizer"]

 Thanks,

HSC can also be used for flowmenter? because I assume the flowmeter noramlly is not high speed.