meaning of input words of flow meters

ABDELAAL said:

dear all,

would you please help me in solving problem with :-

when i connect any device let say flow meter to my plc(s7-300)

the device appears in my hardware catalog and all is fine .but

when i begin to read from it i don't know what does that value mean ? let say series2000 flow meter of emerson it contains 3slots supposed to be for flow density and temp.each of input double word ,now what the value of these input double word mean i mean that value represents flow in what units? or it needs to be converted
to give any meaning? is it real or hex ?...etc

any contribution will help.
regards

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I am not sure i fully understand your question but....

A double word is generally a 32 bit number whereas a single word will be 16 bit

there is a possibility that it is a real number using 2 words but more than likely its just a 32 bit number

if you are reading it back into a PLC then you dont need to do anything with the value just readit and do what you need to do with it

Is that what you were asking ?

DEAR tragically1969 ,

first thank you for your reply. i think that i didn't explain it in a good way.

here we go , I mean that the value I read what does it represent? for example value was 10 what may that mean ?
if i want to compare the value or need to display the value of real flow on let say LCD what shall i write?
is it 10 litre/sec or what?? or the value needs to be evaluated ?

Modern electronics in flow meters are almost universally configurable/programmable for
- engineering units (liters, gallons)
- time units (per second, per minute)
- magnitude of volumetric quantity, where the pulse is 'configured' to represent a specific volume. Multipliers are nearly universally applied, so an output pulse can be configured to represent 10L or 100L or 1000L, or whatever.

I can't tell you how someone else setup the flow meter.

The only way you'll know what volume a pulse from a flow meter represents is to query the flow meter or find the guy who set it up and have him tell you (unless it's an old mechanical positive displacement unit with the volume stamped on the tag).

Dan

Abdellaal,

Flowmeters can be configured (set up) to send flow in many differnt units. The units of the value being sent depends on the brand, model, and set-up of the specific flowmeter. It can be liter/second, liters/minute, liters/hour, gallons/sec, gallons/minute, and so on.

You should get information on the flowmeter. There should be a manual that describes how to set the flowmeter to produce different units. If it was set by someone else, then you must find out how it is set up, and what numbers it is sending.

Once you know the range and units that the number represents, you can convert or scale it to whatever you need.

Here in the U.S., many instruments are specified with an output in miliamperes, with a range of 4 to 20 mA. So for a flowmeter, 0 flow = 4 miliamperes, 100% flow = 20 miliamperes. Again, you have to find out what is 100% or maximum flow for your particular flowmeter.

You also have to know what the input from the flowmeter is (voltage or miliamperes), and how the Siemens S7-300 PLC converts the input to numbers. In other words, for a 4 to 20 mA current input, what range of numbers does the S7-300 convert this to?