Programming Question

[Chris]

I have two controllers contected to louvers used to control air flow and temperature
into our wind tunnel. One controller is a 0 - 10 volt signal and one is
a 0 - 5 volt signal. I would like to write a vi that increases voltage to
one and at the same time decreases voltage to the other. The voltages should
never exceed the 0 - 10/5 parameter. Anyone have any ideas?

Thanks
Chris

[Walter Petermann]

Chris wrote:
>
> I have two controllers contected to louvers used to control air flow and temperature
> into our wind tunnel. One controller is a 0 - 10 volt signal and one is
> a 0 - 5 volt signal. I would like to write a vi that increases voltage to
> one and at the same time decreases voltage to the other. The voltages should
> never exceed the 0 - 10/5 parameter. Anyone have any ideas?
>
> Thanks
> Chris

Chris,
depending on the D-A card you have, you can use different
external reference voltages for the DACs.

On my AO-6, I would use the internal ref on one channel to
give unipolar 0-10, and an external 5v ref on the other for
0-5v output. On this card, the DACs are arranged in pairs
that use the same ref voltage. With this setup then, y
ou would
end up with two pairs of DACs, one pair with 0-5v output ad the
other pair with 0-10.


Walter

[Michael Porter]

This description implies that when one signal is fully on the other is fully off, yes?
If so the solution is simple. Starting with the value of the first controller, say it is
sitting at 8V or 80% of full-scale. subtracting 80 from 100 gives 20, so the second
controller then would be set to 20% of full scale, or 1V. Decreasing the first
controller to 6V or 60% would mean the second controller would be at 40% (100-60), or
2V.

Work it out using the percentages and you'll never have to worry about overshooting your
valid ranges.

Alternately, if the relationship between the two isn't so linear, simply create a lookup
table containing the values for the second controller, and use the first value
controller setting to index into that table.

Mike...

Chris wrote:

> I h
ave two controllers contected to louvers used to control air flow and temperature
> into our wind tunnel. One controller is a 0 - 10 volt signal and one is
> a 0 - 5 volt signal. I would like to write a vi that increases voltage to
> one and at the same time decreases voltage to the other. The voltages should
> never exceed the 0 - 10/5 parameter. Anyone have any ideas?
>
> Thanks
> Chris