Cleveland Motion Controls Classic Series DIN Rail Amplifier Non-Isolated MWI-13466 REV CA - Manual (Page 17)

MAN-13466 R EV CA C LASSIC S ERIES N ON -I SOLATED A MPLIFIER
P AGE 17 OF 26
3.1.2 P OWER A PPLICATION
Apply DC power to the amplifier and use a DC voltmeter to confirm that the supply polarity and voltage is within
the prescribed limits. As soon as is practical, confirm that the excitation voltage is either 5.0 VDC or 10.0 VDC as
appropriate for the type of load cells being used. Promptly identifying any over-voltage condition can help
minimize potential damage to the strain gage elements internal to the transducer. Note that the excitation voltage
may rise to approximately 6.5 VDC if the amplifier is operated without any transducers attached. This voltage will
return to the precisely regulated value when the transducer load is connected.
3.2 T RANSDUCER P OLARITY C HECK
This step is important in identifying transducer or wiring problems early on in the setup procedure. Information
learned in this check will be instrumental in setting the optimum gains for the Instrumentation Amplifier stage.
Measure the -INPUT signal from transducer 1 with a digital voltmeter (DVM) at the input to the amplifier with
respect to the Excitation Return (EXC RET) to confirm that it is roughly 50% of the excitation voltage.
Measure the +INPUT signal from transducer 2 to confirm that it is roughly 50% of the excitation voltage.
If either measurement is less than 45% or greater than 55% of the excitation voltage, then it is likely that the
transducer cable leads have been mis-wired.
Measure the voltage at the +INPUT to confirm that it becomes more positive when a small trial force is applied in
the transducer’s intended force direction. The –INPUT signal should become less positive when the same force is
again applied. If the “sense” of both of these voltages change is incorrect for the way the transducer is mounted,
interchange the load cells wiring for the –INPUT and +INPUT signals. If only a single transducer exhibits the
incorrect “sense, interchange the excitation and excitation return leads on that particular transducer.
Without a calibration force applied to the load cells, measure the “UNLOADED” DC voltage difference between the
+INPUT and –INPUT signals. Use the lowest practical voltmeter scale to provide a meaningful measurement.
Remember or record this measured value for later use.
Apply the intended full-scale force to the load cell and measure the “LOADED” voltage.
Both of these voltages, as well as the difference between these two voltages, help to indicate the best Gain setting
configuration at the first amplification stage. Select the highest possible gain for the first stage that does not result in
saturation (“clipping”) of the transducer signal. If the voltages do not exceed 180mV, then a gain of 25 is
appropriate. Similarly, a lower signal of 35mV could use a higher gain of 125.
Set the IA gain using the Jumper-Switches (refer to section 2.8).
3.3 C ALIBRATION
The following sections describe the calibration process for establishing particular voltages at the +/- 10V analog
output. If you intend to use only the damped meter output, then make that output the focus of your calibration
efforts.
3.3.1 S AFETY C ONSIDERATIONS
Don’t let safety be an afterthought. Before beginning calibration of transducers, review and follow applicable
policies and procedures to ensure worker safety. Machinery must be in a safe state, and you should be aware of
additional hazards that can arise when calibrating higher force transducers.
The following points are important to remember:
•
When dead weights are used to produce a force, always wear steel-toed shoes.
•
When manually handling weights, use safe lifting practices to avoid injury.
•
Size any cordage or straps with an ample safety factor to reduce the chances of failure and falling weights.
•
Consider where the cords and weights will travel should a failure occur.
•
Check that all hardware is mounted with the appropriate fasteners (thread size and pitch, fastener grade,
length of thread engagement).