Im using a 4-20 mA to control a masic meter, but when I want to measure the totalizer i have quite a difference!
I have heard that I can use the pulse output but I can't find what type of input card can I use with simatic or allen bradley?

Thanks

 

Maybe i do not understand the question. But when I have dealt with pulse outputs on totalizing meters before, all it took was a standard digital input card. See, the meter sends out a pulse for every X amt of flow (for me its usually been 1000 gal). So all you have to do in the PLC is count the pulses, and thats how many thousand gallons you've had. Maybe you were just trying to make it too hard.

Oh yeah, and look at your application, if the pulses are expected to be coming quickly, you might need to pony up the dough for a high speed digital input card, but thats unlikely.

-jeff

 

There are two ways of getting totals. One is to integrate the rate over time( if the 4-20 ma signal is a rate then after scaling you coud integrate it. Integration would be accomplished by a subroutine that samples the value every delta t, multiplies the sample by delta t, and then running a continous sum of the results to get a total. The other way to get totals is to count pulses from a device that gives a pulse for every unit quantity( 1 pulse /gallon etc ). To do this you have to know the Pulse output circuit. Some are TTL,others are 0-24vdc, some are open collector,some are relay. Once this is known the PLC rep will pick out a compatable input module.

 

What are the characteristics of the pulse?

On/off delay for Allen-Bradley SLC 500 standard DC input modules is 8 msec on / 8 msec off, and for the fast response modules (1746-ITB16 and -ITV16) it is 0.3 msec on / 0.5 msec off. (up to 1 KHz according to A-B).

If you need something faster, try the high-speed counter module (1746-HSCE2), which can count up to +/-8,388,607 and can handle rates up to 1 MHz. We've used this module for quite a few applications with quadrature encoders, but it can also handle single pulses.

I didn't check the discrete I/O ratings for PLC 5. If you need a high speed counter module for PLC 5, it's a 1771-VHSC. We've had great success with this module also.

 

I suppose your application may be a totalizer for a water flow or other similar things.

There are 2 kinds of pulse input. One is high speed counter and the other one is just ordinary digital input. The latter is more common as totalizer is usually used for a general reading over a period of time.

If this is the case, for SLC500, 1746-IB16 is enough for your application. Anyway, the scanning rate of every point on the same digital input module can be as accurate as to the scale of 100ms. Do your pulses come that fast?