DAQmx Create Scale doesn't work

[PatrikLiu]

Dear all,

I added a linear scale to channel, but the amplitude of signal in waveform graph didn't change. Could you help me fix the problem, please? Thank you so much!

[PsyenceFact]

Hi Patrik and welcome to the forums!

Are you using a simulated DAQmx device?  I'm not sure whether the scale makes any difference to the simulated input values.  The guidelines for using a simulated device state that the analog input data is always a full scale sine wave with 3 % of full scale noise.

PsyenceFact

[PatrikLiu]

Yes, I am using a simulated device. Do you mean I should use a real one? I will try it today. Thank you!

[PatrikLiu]

But I think the scale should work this way: if the signal is from -5V to 5V (NI9234), the final value in waveform should be -10 V to 10V with a scale of 2. Is it correct?

[crossrulz · Accepted solution]

---

@PatrikLiu wrote:

But I think the scale should work this way: if the signal is from -5V to 5V (NI9234), the final value in waveform should be -10 V to 10V with a scale of 2. Is it correct?

---

But what you put in for the Max and Min on the Create Virtual Channel are the values AFTER the scale has been applied, not the raw voltage.  So your Max and Min should then be +10V and -10V.  And it is then those values that are used by the simulated DAQ.

[PsyenceFact]

As usual, crossrulz is absolutely correct!

I tested with a simulated USB-4431 which has a maximum voltage range of +/-10 V.  With the custom scale disconnected and using units of Volts results in a simulated signal that matches the input Max and Min Voltage and gives error -200077 if the range exceeds +/-10 V.  With the custom scale connected and using units of From Custom Scale results in a simulated signal that matches the input Max and Min Voltage and gives error -200077 if the range exceeds +/-20 V.

I hope this makes things clear.

PsyenceFact

[PatrikLiu]

Yes, you are right. I read the explanation of Max and Min in help and found it is exactly what you mean. Thank you so much!

[PatrikLiu]

I tested as you did and got the same result. Thank you so much! The signal never exceeds the limit. Anyhow, it is clear now.

[Fulvio]

Dear all,

I don't understand where the problem is, it seems trivial but unfortunately it is not.
I am acquiring a signal in volts and I want to convert it to another scale (Nm).
The problem is in the "scaled values" if the coefficient changes of one orders of magnitude works,  from two orders of magnitude the data changes apparently without logic.
What am I missing ?!

the original value around -0.667

times 10 = -6.67

times 100 = -21.57 ?!?

times 1000 = -215.72

times 10000 = -2157.21

Thank you all.

[Kevin_Price]

Are you *certain* that the raw voltage input value was the same for all the trials?  One plausible explanation is that there was an actual shift in the raw voltage after the first 2 trials that remained for the next 3.

Be sure you have a steady constant voltage source (a battery perhaps?) wired to the corresponding input when you run the next set of trials.

-Kevin P