Dataq DI-720-EN, User Manual

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DI–720/DI–722/DI–730 Series User Manual
Accessories
86
DI-5B38 Strain Gage Input Modules, Narrow & Wide Bandwidth
Each DI-5B38 Strain Gage input module provides a single channel of Strain Gage input which is filtered, isolated,
amplified, and converted to a high level analog voltage output (see block diagram). This voltage output is logic
switch controlled, which allows these modules to share a common analog bus without the requirement of external
multiplexers.
The DI-5B modules are designed with a completely isolated computer side circuit which can be floated to ±50V from
Power Common, pin 16. This complete isolation means that no connection is required between I/O Common and
Power Common for proper operation of the output switch. If desired, the output switch can be turned on continuously
by simply connecting pin 22, the Read-Enable pin to I/O Common, pin 19.
The DI-5B38 can interface to full- or half-bridge transducers with a nominal resistance of 100
Ω
to 10k
Ω
. A matched
pair of bridge-completion resistors (to ±1mV at +10V excitation) allows use of low cost half- or quarter-bridge trans-
ducers. On wide bandwidth modules, the 10kHz bandwidth allows measurement of high speed processes such as
vibration analysis.
Strain Gage excitation is provided from the module by a very stable 10V or 3.333V source. The excitation supply is
fully isolated, allowing the amplifier inputs to operate over the full range of the excitation voltage. Full scale sensitiv-
ities of 2mV/V, 3mV/V or 10mV/V are offered. With 10V excitation, this results in a ±20mV, ±30mV or ±100mV full
scale input range.
On wide bandwidth modules, the input signal is processed through a preamplifier on the field side of the isolation
barrier. This preamplifier has a gain-bandwidth product of 5MHz and is bandwidth limited to 10kHz. On all modules,
after initial field side filtering, the input signal is chopped by a proprietary chopper circuit. Isolation is provided by
transformer coupling, again using a proprietary technique to suppress transmission of common mode spikes or
surges. The module is powered from +5VDC, ±5%.
Special input circuits on the DI-5B38 module provide protection of the signal inputs and the isolated excitation sup-
ply up to 240VAC.