Measurement Computing Data Translation DT3034, Руководство пользователя

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Chapter 6
74
Input Ranges and Gains
Each channel on the DT3034 board can measure unipolar and bipolar analog input signals. A
unipolar signal is always positive (0 to 10 V on DT3034 boards), while a bipolar signal extends
between the negative and positive peak values (±10 V on DT3034 boards).
Through software, specify the range as 0 to 10 V for unipolar signals or

10 V to +10 V for
bipolar signals. Note that the range applies to the entire analog input subsystem, not to a
specific channel.
DT3034 boards also provide gains 1, 2, 4, and 8, which are programmable per channel. Table 4
lists the effective ranges supported by DT3034 boards using these gains.
For each channel, choose the gain that has the smallest effective range that includes the signal
you want to measure. For example, if the range of your analog input signal is ±1.5 V, specify a
range of

10 V to +10 V for the board and use a gain of 4 for the channel; the effective input
range for this channel is then ±2.5 V, which provides the best sampling accuracy for that
channel.
The simplest way to specify gain for a single channel is to specify the gain for a single-value
analog input operation using software; refer to
page 76 for more information on single-value
operations.
If you are using an analog input channel list, you can use software to specify the gain for each
analog input channel entry in the analog input channel list.
Note: For analog input channel 32 (the 16 digital I/O channels) in the channel list, specify a
gain of 1.
A/D Sample Clock Sources
DT3034 boards provide two clock sources for pacing analog input operations in continuous
mode:
• An internal A/D sample clock that uses the 24-bit A/D Counter on the board
• An external A/D sample clock that you can connect to the screw terminal panel
Table 4: Gains and Effective Ranges
Gain
Unipolar Analog
Input Range
Bipolar Analog
Input Range
1 0 to 10 V ±10 V
2 0 to 5 V ±5 V
4 0 to 2.5 V ±2.5 V
8 0 to 1.25 V ±1.25 V