DAQmx Task Gives Error -200077 When Creating a Custom Scale

Updated May 17, 2018

Reported In

Hardware

  • USB-6259
  • NI-9207

Driver

  • NI-DAQmx

Issue Details

I am trying to create a custom scale for the signals acquired from my NI DAQ device. I have created a task in Measurement & Automation Explorer (NI MAX), and I have created a custom scale. However, when I try to save or run the task, I am get the following error: 

Error -200077 occurred at DAQ Assistant 

Possible Reason(s): 
Measurements: Requested value is not a supported value for this property.


How can I fix this?

Solution

When the signal input range does not match the scaled values, as in the figure below, error -200077 can occur.

The signal input values of the device are represented with the units as the scaled values. For example, if your scaled values range is 0 to 200V and your pre-scaled value range is -5 to 5 V, then the signal input range must also be 0 to 200V and not +/-5V. In other words, when you create a custom scale, the scaled values must match the signal input value.

Additional Information

  • Linear Scale
Slope and the Y-intercept define the new values, where the Slope converts from volts to the scaled units and the Y-intercept adjusts for any offset in the scaled units.
As mentioned, the NI 9237 reads input in mV (notice the default Pre-Scaled units below are volts).  There is not a mV setting; therefore, remember to convert the reading from mV to volts.
Slope can be determined by the maximum value of the transducer divided by the transducer's rated output (R.O).

Ex: 100 lb tension/compression load cell with 2 mV/V R.O., an offset of 5 lbs, where compression displays a negative value.

Note:  The linear scale is the only scaling option that enables the use of a negative slope. 

slope = 100 lbs /.002 V/V = 50000 lbs/(V/V)

The equation for this situation would be y = -50000 * X + 5

Since the maximum/minimum values for X, the measured value, are +/- .002 V/V, the new Signal Input Range is:

maximum = 50000 lbs/(V/V )* .002 V/V + 5 lbs = 105 lbs
minimum =  50000 lbs/(V/V) *  -.002 V/V + 5 lbs = -95 lbs

Remember that you will no longer have a symmetric Signal Input Range, shown below in red, when using an intercept. Also verify the custom scale is applied and the new Scaled Units are displayed correctly, shown below in blue.

  • Map Ranges Scale

This scale is convenient for directly assigning Pre-Scaled Values to their corresponding Scaled Values, where the maximum and minimum Pre-Scaled Values are +/- the transducer's Rated Output (R.O.) in volts.

Ex:  A 100 lb tension/compression load cell with a 2 mV/V R.O.

Note: Remember to verify a custom scale is selected and the new units appear as expected in the DAQmx task as shown in blue in Figure 2.
 

  • Table Scale

A Table Scale can be used similar to a Map Ranges Scale by directly assigning the Scaled Values.  However it can also be used to input the calibration values from the Certificate of Calibration provided with the transducer. 

Ex:  The Certificate of Calibration  for a load cell lists the load as -100 lbs and the mV/V as -1.95, as well as, 100 lbs and 1.98 mV/V.  

 

Select Add and enter - 0.00195 for Pre-Scaled and -100 for Scaled.  Repeat for the next set of values with .00198 for Pre-Scaled and 100 for Scaled.

Note: Remember to verify a custom scale is selected and the new units appear as expected in the DAQmx task as shown in blue in the Task Configuration.

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