National Instruments Module SCXI-1125 Uživatelský manuál stáhnout pdf (Strana 60)

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Chapter 5 Using the SCXI-1125

Perform Offset Null Compensation Using Traditional NI-DAQ (Legacy)

C API

After configuring the system settings and module properties, you

can perform an offset null compensation programmatically using

SCXI_Calibrate. SCXI_Calibrate takes measurements and adjusts the

coarse and fine offset null potentiometers to minimize or eliminate any

electrical offset for a channel. Repeat this process for each channel by

calling the

SCXI_Calibrate function in a loop. Use the resulting

imbalance in your application as a software correction factor by

determining the residual voltage from the imbalance, and subtracting this

residual offset from each future measurement. For more information

regarding the operation of

SCXI_Calibrate, refer to the Traditional

NI-DAQ (Legacy) Function Reference Help installed by default in Start»

Programs»National Instruments»NI-DAQ.

Perform Acquisition Using Traditional NI-DAQ (Legacy) C API

There are several NI-DAQ functions you can use to take measurements.

Usually in SCXI the preference is to take multiple samples from multiple

channels using the

SCAN_Op function. SCAN_Op performs a synchronous,

multiple-channel scanned data acquisition operation.

SCAN_Op does not

return until Traditional NI-DAQ (Legacy) acquires all the data or an

acquisition error occurs (MIO, AI, and DSA devices only). For this reason,

it is sometimes useful to use

SCAN_Op in conjunction with the function

Timeout_Config, which establishes a timeout limit synchronous

functions to ensure that these functions eventually return control to your

application. After acquiring data using

SCAN_Op, the resultant data is not

organized by channel, so you should demultiplex the data using

SCAN_Demux. SCAN_Demux rearranges, or demultiplexes, data acquired by

SCAN_Op into row-major order, meaning each row of the array holding

Table 5-8. NI-DAQ Functions Used to Configure SCXI-1125

Channel

Setting

NI-DAQ Function to Use

Significant

Parameters

Possible Parameters

Values

Gain

SCXI_Set_Gain

f64 gain

(gain setting)

1, 2, 5, 10, 20, 50, 100,

200, 250, 500, 1000,

2000

Bandwidth

SCXI_Configure_Filter

f64 freq

(filter cutoff

frequency if

filterMode = 1)

4.0, 10,000.0 Hz

1 2 ... 55 56 57 58 59 60 61 62 63 64 65 ... 100 101

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