Rice Lake Load Cells - 441/442 Bridgesensor Load Cell Input to Analog Out - Manual

441 and 442 Bridgesensor
Load Cell Input to Analog Output
FEATURES
• Input/Output ranges and excitation voltage are
selectable by easy-access rotary switches.
• Non-interactive zero and span control.
• Offset switch allows cancelling or “taring” of
nonzero deadweights.
• Excitation voltage 10 Volt/115 mA drives up to
four 350-ohm bridges.
• Input/Output LoopTracker TM LED’s show
input/output status.
• Functional test pushbutton with fixed level
output to facilitate setup and troubleshooting.
• Full isolation (Input/Output Power) eliminates
the effects of ground loops and noise.
• LIFETIME WARRANTY
FUNCTIONAL DESCRIPTION
The 441/442 Bridgesensor accepts a strain gauge (bridge) in-
put and provides an analog DC voltage or current output. In
addition, the circuitry contains a stable source of excitation
voltage for use with bridge-type transducers such as strain
gauges, load cells, and similar devices.
The circuitry includes filtering and processing to allow ef-
fective use of low-level transducers in the noisy environments
common in industrial applications. The 441/442 Bridgesensor
allows user selection, via four rotary and one slide switch, of
most popular input and output ranges as well as nine differ-
ent excitation voltages to cover most any bridge transmitter
application. Ranging and setup is done from a simple table
which is used to determine the switch settings. In addition to
field-ranging the, 441/442 Bridgesensor features an excita-
tion source which includes “sense” lead capability to cancel
the effects of leadwire resistance. The excitation source has
10 volt/115 mA current capability for driving up to four 350
ohm bridges.
Rotary-switch selection of offset or tare up to
±
100% of span
may be selected without opening the case. The Functional
Test Pushbutton provides a fixed output, independent of the
input, when held depressed. The test output level can be set
by a top-accessible, multi-turn potentiometer. Multi-turn ad-
justments are also standard for Zero, Span, and Excitation
Trim. The Zero/Span are non-interactive for simplified cali-
bration.
PRINCIPLES OF OPERATION
A stable voltage reference is applied to an amplifier whose
gain is selected by Switch C (Excitation Voltage). This am-
plifier includes a multi-turn adjustment (Excitation Fine Ad-
just). An output buffer with 120 mA current capability fol-
lows, and the output of this buffer provides the bridge excita-
tion voltage. An additional input (“sense” lead) monitors the
voltage drop in the bridge leads and automatically compen-
sates for losses.
The bridge inputs of the module are filtered and applied to a
differential amplifier which cancels the common mode volt-
ages. This amplifier output is applied to a stage whose gain
or attenuation is controlled by Switch E (Input Range) so that
the different input ranges are converted to a usable internal
range.
Once the span has been established, the zero/span of this sig-
nal are adjustable over a range of approximately
±
15% with-
out interaction. This signal is then applied to an adder stage
whose additional inputs are a DC offset level determined by
Switch D (Offset).
At this point, if the TEST pushbutton is pressed, a test volt-
age is inserted which overrides any input. This voltage is set
by the Test Cal control on top of the module.
The input signal is then optically coupled to provide galvanic
isolation between input/output.
Finally, the output stage gain and “zero” level are controlled
by Switch B (Output Range) to provide one of the “standard”
output ranges. This stage configuration is selected by Switch
A to provide either a voltage or a current output. Switches A
and B together select the type of output and its magnitude.
CALIBRATION
39023
2.38"
2.75"
1.75"
Case Dimensions