24/7 Data Acquisition Wildcard Users Guide

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Starting a Conversion

After you initialize the 24/7 Data Acquisition Wildcard and specify the reference voltage, you can calibrate, configure, and start converting samples using Start_Conversion. An alternative routine, Start_Conv_With_Values, allows you to forgo the calibration process and use already determined calibration coefficients instead. Each of these routines are discussed in turn.

Calibrating and Starting a Conversion

To use any of the channels listed in Table 1, the channel must first be calibrated. You should also perform a calibration whenever the temperature or supply voltage changes significantly, or whenever you change the gain, sample frequency, or polarity options. Start_Conversion calibrates the analog to digital converter with the specified options and calibration type and initiates continuous sampling and conversion. Start_Conversion requires seven parameters to configure the sample frequency, gain, calibration type, polarity, resolution, burnout current option, and channel: each of which is discussed in detail in the following paragraphs.Start_Conversion also performs extensive error checking on each parameter to ensure that each option is valid. Table 3 lists the possible error codes returned by Start_Conversion.

Table 3: Error Codes Returned By Start Conversion

Starting A Conversion with Predetermined Calibration Coefficients

Once you calibrate a channel using Start_Conversion, you do not have to repeat the calibration unless the temperature or power supply voltage changes. To start a conversion without a calibration use Start_Conv_With_Values. This routine allows you to quickly switch back and forth between channels without recalibrating the channel each time. Start_Conv_With_Values requires nine parameters: the full scale calibration values, zero scale calibration values, sample frequency, gain, polarity, resolution, burnout current option, synchronization option, and channel.

To call Start_Conv_With_Values you need valid calibration coefficients. You can obtain these coefficients by calling Read_Zero_Cal and Read_FS_Cal after Start_Conversion is called. Be sure to save all seven parameters that specify the channel information (such as the gain, resolution, and sample frequency) along with the calibration values. See the example program in the Example Code Section for an example application using Start_Conv_With_Values to obtain and store 10 samples to an array from four channels.

No error checking is done in Start_Conv_With_Values to minimize the time required to switch from one channel to another and because error checking would already have been done by Start_Conversion.

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