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Chapter 2 Function Reference — SCXI_Set_Threshold
NI-DAQ FRM for PC Compatibles 2-364
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National Instruments Corporation
SCXI_Set_Threshold
Format
status = SCXI_Set_Threshold (SCXIChassisID, moduleSlot, channel, level, hysteresis)
Purpose
Sets the high and low threshold values for the SCXI-1126 frequency-to-voltage module.
Parameters
Input
Parameter Discussion
channel is the number of the channel on the module.
Range: 0 to n–1, where n is the number of channels available on the module.
–1 for all channels on the modules.
level is the middle of the window between the high and low threshold values. For example,
to set a low threshold of 1.0 V and a high threshold of 3.0 V, you would specify a level of
(1.0 + 3.0)/2 = 2.0 V. level should be between –0.5 and 4.48 V.
hysteresis is the size of the window between high and low threshold values. The low
threshold value plus hysteresis equals the high threshold value. For example, for a low
threshold value of 1.0 V and a high threshold value of 3.0 V, you would specify a hysteresis
of 3.0 – 1.0 = 2.0 V. hysteresis should be between 0 and 4.98 V.
Using This Function
Currently, only the SCXI-1126 supports this function. The SCXI-1126 uses the high and low
threshold values to transform a periodic input signal into a square wave with the same
frequency. When the input signal rises above the high threshold value, the square wave
triggers high. When the input signal falls below the low threshold value, the square wave
Name Type Description
SCXIchassisID i16 SCXI chassis ID number
moduleSlot i16 SCXI module slot number
channel i16 analog input channel
level f64 specifies the average of the desired high and low
threshold values
hysteresis f64 the difference between the high and low threshold
values