Data Translation DT9837, User Manual

Page: 69 / 150

Principles of Operation
69
Input Ranges and Gains
The DT9837 Series modules provide an input range of ±10 V and software-selectable gains of 1
and 10. This provides effective input ranges of ±10 V (when the gain is 1) and ±1 V (when the
gain is 10).
IEPE Functions
Applications that require accelerometer, vibration, noise, or sonar measurements
often use IEPE
sens
ors. IEPE conditioning is built-in to the analog input circuitry of the DT9837 Series
modules. The modules support the following software-programmable IEPE functions for each
of the four analog inputs:
• Excitation current source – The DT9837, DT9837A, and DT9837B modules provide an
internal excitation current source of 4 mA. The DT9837C module provides an internal
excitation current source of 2 mA. You can enable or disable the use of a internal excitation
current source using software. By default, the excitation current source is disabled.
• Coupling type – You can select whether AC coupling or DC coupling is used. By default,
DC coupling is selected for the DT9837, DT9837A, and DT9837C modules, and AC
coupling is selected for the DT9837B module.
Note: If you enable the use of the internal excitation current source, it is recommended
that you choose AC coupling.
The DT9837C also provides a 1 Hz high-pass filter.
You can change the IEPE settings using the Open Layers Control Panel applet, described on
page 36 , or by writing to the registers of the module, as described on Appendix C starting on
page 135 . For information on wiring IEPE inputs, refer to page 44 .
For the DT9837A, you can also use the Control Panel to keep the module’s high-power
circuitry always turned on to minimize any settling time errors related to the IEPE current
source. Refer to
page 36 for more information.
Input Resolution
The resolution of the analog input channels is fixed at 24 bits; you cannot specify the
resolution in software.
Input Clock Source
The DT9837 Series modules support an internal clock, which is derived from the USB clock.
Use software to specify the internal clock source and the frequency at which to pace the input
and output operations and to start the sample clock. For the DT9837 and DT9837A, the
sampling frequency ranges from 195.3 Hz to 52.734 kHz. For the DT9837B and DT9837C, the
sampling frequency ranges from 195.3 Hz to 105.469 kHz.