Ladder Logic for Flow Meter Totalizer

This is a PLC Ladder Logic to calculate the flow rate and also count the total flow or totalizer.

Flow Meter Totalizer

Ladder Logic for Flow Meter Totalizer

By using some math, bit and comparator functions, prepare a PLC program that can calculate the flow rate of gas and also count the total flow.

Flow Totalizer Graphics

Problem Solution:

  • To calculate flow, first we have to measure differential pressure.
  • To measure differential pressure, Differential Pressure transmitter installed at pipe line.
  • Range of DP transmitter is 0-1000 Pa.
  • Output of this transmitter is in standard electrical signal which is 4-20 mA. Convert this signal into digital signal by connecting transmitter to AI module of PLC.
  • To find the Flow Rate, Apply formula ( Flow Rate = k √∆P ) given by the designer using math block in PLC.
  • Prepare a logic for Flow totalizer using math function in PLC.


In this example, we are assuming the transmitter output 4-20 mA is equivalent to “Differential Pressure” instead of direct flow reading. So we are applying the square root function in PLC to derive the equivalent flow rate from this measured “differential pressure”.

PLC Address & Data Types

Flow Totalizer Data Type

PLC Ladder Logic

Network 1 :

PLC Conversion Block from Analog Signal into Digital

In this Network 1, we are converting Analog Signal of the Differential Pressure Transmitter which is in 4 – 20 mA to digital value 0-1000 Pa.

Network 2 :

Flow Rate Formula in PLC

In the Network 2, We are finding Flow Rate by applying formula( Flow Rate = k √∆P ). Where k is the constant which is 10000 in my case and ∆P is the differential pressure in Pascal, which we are getting from the above network.

So we are using square root block and multiplication block to achieve this formula.

The unit of flow rate is m3/hr.

Network 3 :

Ladder Logic to Find Flow Rate

Now this is tricky network, if you count the total flow then you must do increment the flow rate at every minimum time frame whichever is possible.

So here I have used clock memory here and minimum possibility of time frame of my PLC is 0.1s (seconds). So I have to find out the flow rate at 0.1s for that.

I have used the below formula to find out the flow rate at 0.1s

Flow Totalizer Formula

Network 4 :

Ladder Logic for Total Flow

In this Network 4, we are doing addition of flow rate at 0.1s at every 0.1s and save it to Total_Flow.

This is the totalizer of the flow.

Author : Hiral Patel

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