Totalizing an analog signal

I have a Mitsubishi Q Series PLC and a E-terminal. I have an analog from a magometer 4-20ma going into my plc. I just need the PLC to read the analog signal and then display a total flow for the day and for the week. I know how to get the HMI to read it but not sure how to do the gpm totals. First I need to know the total GPM for the day and then I need to know the Total GPM for the week. Can any one please help me to do this.

Thanks
Allen

Dear Allen,
This can be done by little calculation in your plc program.If you know the flow rate=x gph, convert it to gps.

Total=0;count=0;
Total=total+gps;
Samplecount=Samplecount+1;
Total=Total/Samplecount;

I think this will help you to start atleast,
bye

Allen.
Apel's method will work but you will probably find that there is a significant difference between the value you calculate and the value the users read off the front of the meter. As this is an integrating instrument a small error on the analogue signal will eventually become a big error in the total. The best way I have found to solve this is to use a pulse from the meter and calculate the flowrate using the time between pulses rather than trying to integrate the analogue signal. Most flowmeters will give you a pulse output so I would recommend you look at this option.
Andyr

I agree with Andy 100%. Use the analog for instantaneous flow and totalize off of the pulses. Make sure the pulse duration is long enough for the PLC input to see it.


Marc

Agree with Andy and Marc, you need pulse signal from the meter. If it's unavailable, Apel's way is ok but you have to call the program every second, just one shot/scan calling per second. But PLC has limitation, because of its cycle time or signal disturbance. It can be lead to significant diference with the actual meter.

I second Andy's (and the others)sentiment and can tell you what he has said is 100% true. We had to implement a pulse counter in a similar situation and are now never "OFF" or different by more than the pulse increment when comparing the magmeter controller display and SCADA display.