pre-scaled range 4 to 20mA no allowed

[Will_Crowe]

I am trying to set up a custom range that maps a pre-scaled value of 4-20mA from the sensor to an output range of 0-6kW. I can choose 'Amps' as the pre-scaled range units and I can enter 0.02 as the maximum pre-scaled value, but when I select 0.004 as the minimum value, it jumps to 0 every time on the graph. It messes up the measurement as well. It won't allow that as the minimum value.

I have tried a few other things and it seems that Measurement and Automation Explorer won't allow a range with max and min at different places of decimals.For example:

Min 0, Max 0.02 - OK.

Min 0.01, Max 0.02 - OK

Min 0.004, Max 0.02 - Not OK, Min jumps to 0.

Min 0.01, Max 0.025 - Not OK, Max jumps to 0.03.

The obvious thing to try would be Min 0.004, Max 0.020 but this doesn't work either.

This seems very odd to me as 4-20mA is a measurement standard. Am I missing something really obvious?

I could just bring in the values raw and scale them in labview but I have always pre-scaled values in MAX and would prefer to do it that way. Surely this is posssible?

Any help would be greatly appreciated.

BB

[aeastet]

Did you set it up as voltage or current. That might be the reason that it will not allow you to do that.

[Will_Crowe]

Tim,

Thanks for the reply. I did choose 'Amps' as the units, not 'Volts' so that doesn't seem to be the problem.

If you try it yourself in MAX, you will find the same thing. The ranges snap to rounded off values. It's quite mad, particularly when it does not announce to you that it is doing this.

Barry

[GerdW]

Hi Will,

apply the scale in LabVIEW to the DAQmx task, here you will be able to apply any value you like.

Possible reason for this problem: MAX only shows 2 decimal digits and maybe also rounds any number to that scheme!?

[aeastet]

When you set up the channel in max you should have had to pick what kind of channel that you wanted. voltage, current temperature etc...

What did you pick?

[Will_Crowe]

Tim,

I set it up as a current channel alright.

Having said that, the scale is set up separately. You set up a scale and then it appears in a pulldown menu and you apply it to whatever task you want. Is there some way of setting up the scale for the channel specifically rather than applying it to the task?

Barry

[Will_Crowe]

Thanks GerdW,

I tried that also but I was led back into the same options for setting up the scale and again (as you suggest) there is some 'rounding' going on which seems very odd.

I contacted NI and the girl got back to me to say she was finding the same thing and would dig further. Will let you know what she turns up and keep trying things.

Will

[Will_Crowe]

Tim,

Sorry, I got confused in that last post. I had been applying the scale to individual channels not just overall tasks.

Will