PID Loop and Totalizer Using Analog Input

Hello Everyone

I need to solve the following tasks:

1. Make totalizer using Analog Input signal.

I have MD+ series controller with AI card with Flow Transmitters wired on it. Transmitter measures current flow rate. Engineering units of FT is [kg/hr]

Which block in Control Strategie is right to use to make Totalizer to count

- summary(Total) flow rate of last 2 hours in [kg]

- summary flow  rate of a 24 hours (last day, use 00:00 PST as base point) [tonnes/day]

2. Two flow runs , with an oil in first pipe and depressant in second pipe, with Flow Transmitters, which measuring current flow rate, installed on each pipe as well. Motor operated valve is used to inject depressant into oil pipe. By technology it is needed to inject 200 gramms of Depressant per each tonne of oil. How will PID block for MOV be set? What I think is to add two PID`s and make cascade mode of operating of:

PID1, with following parameters:

PV - FT installed on depressator pipe (4-20mA)

SP - ?

OUT - will be connected to SP of PID2

PID2, with following parameters

PV - FT installed on oil pipe (4-20mA)

SP - ?

OUT - MOV

Kindly advice if have related experience. Thank you in advance!

Daniyar Mamenov

Design & Application Engineer

Projects - ME&CIS

INTECH Process Automation - Kazakhstan Office

  • Hi Daniyar, we normally use an integrator function block to perform the totalising function. This can accumulate the number of kilograms. For your second question you should probably consider using ratio control function block. The oil in your first pipe will be the wild flow input. The ratio controller will then control the setpoint of the second PID to keep it at a known ratio to the first PID flow input. Hope this helps. If you have a system based on PCSD then you will find control modules which provide both ratio control and totalizing.