Measurement Computing Data Translation DT9857, Руководство пользователя

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Chapter 8
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Calibrating the Analog Input Subsystem
This section describes how to use the calibration utility to calibrate the analog input
subsystem of a DT9857 or DT9857E module.
DT9857 and DT9857E modules have separate calibration for each A/D input channel.
Warming up the Module
Before calibrating the analog input circuitry, ensure that the module has been powered on for
at least one hour.
Connecting a Precision Voltage Source
To calibrate the analog input circuitry, you need to connect an ex9.3750 V precision
voltage source to the DT9857 or DT9857E module. Connect the precision voltage source to the
first channel you want to calibrate; for example, Analog In 0 (AD Ch0).
Using the Auto-Calibration Procedure
Auto-calibration is the easiest to use and is the recommended calibration method. To
auto-calibrate the analog input subsystem, do the following:
1. Select the A/D Calibration tab of the calibration utility.
2. Under the Calibration Settings area of the window, select the sampling frequency, in
Hertz, and the gain that you want to use.
Notes: The DT9857 and DT9857E modules have two power modes: low power mode and
high power mode. Low power mode is calibrated when you specify a sampling frequency
less than 52.734 kHz. High power mode is calibrated when you specify a sampling
frequency greater than 52.734 kHz. Ensure that you calibrate the board for both high and
low power mode if you are using sampling frequencies below and above 52.734 kHz.
By default, this utility uses DC coupling with the current source disabled. This is the
recommended setting for most users. While changing these settings is not advised for
most users, users with unique applications can change these settings by clicking the
Advanced button.
3. Under the Automatic Calibration area of the window, select the channel that you want to
calibrate from the
Type of Calibration drop-down list box, and then click the Start button.
A message appears notifying you to verify that 0.0000 V is applied to the channel.
4. Verify that the supplied voltage to your selected channel is 0.0000 V, and then click OK .
The offset value is calibrated. When the offset calibration is complete, a message appears notifying
you to set the input voltage of the channel to +9.3750 V.
5. Check that the supplied voltage to your selected channel is +9.3750 V, and then click OK .
The gain value is calibrated and a completion message appears.