Flow Rate Calculations Siemens S7

Siemens S7-300 CPU315-2DP

Hi Guys

I need to accurately calculate the flow rate of a material that is passing through a totalised flow meter. At the moment I have a simple 1 second timer setup so that it calculates the difference between a snapshot DINT of the last total and the current DINT total then * 60 to give me the flow rate per minute.

This is not very stable due to the scan times of the PLC. Is there another way so that the scan times of the PLC will not affect the calculation of the flow rate, maybe by using the system time in the calculations or calling system function.

If possible please provide code examples in your replys.

Cheers

Invest in a totalizing flow meter! You've already bought it 10 times over through the waste of time.

OB35 is the timed interrupt block and you can set how often this block is called in the h/w config. This will give you a reliable steady time base for sampling your signals.

Never delt with s7 300 but with s7 400 series you can go to library (standared blocks ) apply fc 105 i think its scaling block and wire there your PIW ( 4-20Ma ) from your flometer depending on your parameterization shld give you acurately the flow rate did it with our feeding system .