Hi,

We are studying on flow calculations of natural gas by using MOSCAD Motorola RTUs. RTU gets two kinds of pulses from one source. One is high frequency and the other is low. The problem is that when we try to calculate the flow by using both pulses, there is a big difference. Especially in low flow calculation. The flow calculation standard we use is AGA. Is there anybody who has documentation or suggestion about this subject? I will be very happy if anybody helps me.

Thanks,
Murat

Scada Software Engineer

 

Murat,

You need to understand the device you are connecting to. You are most likely connecting to a dual rotor turbine meter that has an algorithm to determine the actual flow rate through both rotors.

Check with the manufacturer of the turbine meter or drop me an email for more detail.

[email protected]
http://www.emersonprocess.com/flow

 

Are you using the AGA code within the Moscad (happens to be very good)?

Usually the device which is transmitting the pulses will have a given pulse scaling factor (x pulses / scfm), if your device outputs 1p/scfm and your flowing at a 1000scfm, then you will have 1000pulses per minute or roughly (16.6667 pps), count the number of pulses per minute, or get a converter to take the pulse to a 4-20 ma signal, then you can integrate the signal and get flow totalization, do averaging and such. (if I am not mistaken, many of the high end meters provide a 4-20ma output which converted internal fro the pulse ciruit of the meter).

Make sure you also use the high speed counter input for the faster pulses. Heck if you have 1000 pulses per scfm and your flowing at 1000scfm, then a normal counter input will not work.

The device your connected to has already done the calcs for the gas flow ,you just need to count the pulses over a period of time and then do a little math.

MJH