Using a 4ma-20ma velocity meter with cfp-ai-110 field point module

[kevin91172]

We are working on a heat exchanger tude tester using a 4-20ma veocity meter.We wired accordind to the manual and we are seeing variations when we ramp up and down our blower.We found a help file about the tank level,4ma=0 feet---20ma= 50 feet and the equation with it, but we are still scratching our heads.The meter read 0-2000 on the previous tester .What will be the way to go on fixing our 4-20ma offset and how do we get a real velocity measurement in our Labveiw?

[Laura F.]

Hello Kevin,

I am afraid I will need more information about your application to fully understand your question.  You have a velocity meter that outputs 4-20 mA and you know how to apply a scale to convert this to a velocity measurement.  What kind of variations are you seeing when you ramp your motor? 

You say that your previous meter read 0 - 2000.  What units is this? 

What do you mean by "fixing the 4-20 mA offset"?  My impression is that the meter outputs in this range, so this is not an offset.  To convert this to velocity, use the equation given in LabVIEW to scale the current value appropriately.

Regards,

Laura

[kevin91172]

The 0-2000 CFM,and could you point me to an equation for the 4-20ma to get my correct readings?Do I multiple by 100,000 the ma?

[Laura F.]

Hi Kevin,

Sorry for the confusion.  If your meter outputs 4-20 mA, the manufacturer of the meter should provide you with some sort of scale for converting this current signal into the units you are interested in.  I am not sure if those units are distance or velocity, but the documentation of your meter should be able to clear this up for you.  Then, in LabVIEW, you can implement this scale to convert current to the appropriate units.

Regards,

Laura

[JPal]

If output of the level transmitter is linear like it usually is, you should use following scaling:

Level [ft] = (Input signal [mA] - 4 [mA]) x 3,125


Multiplier of 3,125 comes from:

50 ft / (20 mA - 4 mA) = 3,125