Model 3770
DC STRAIN GAGE PANEL METER
4.
CALIBRATION – Shunt Calibration
This section contains the instructions for calibrating the 3770 using the Shunt calibration method.
( a )
Connect Power, Sensor and Analog terminals as required. Apply power. The front-panel digital
display should light indicating the application of the AC input power. Allow 10 minutes of warm
up for stabilization of transducer characteristics. Remove the front panel cover of the 3770 unit
which is held in place by the two small Phillip head screws.
Note: The 3770 unit has an internal 59K Shunt resistor installed within the unit. If a different
resistor value is to be used to correspond to the transducer’s calibration sheet; install the resistor
on the rear J1 terminals provided and place the Analog Control Switch 5 to External. Shunt
calibration will only activate if the CAL Sense line is connected to the + or – Signal lines on the
transducer input connector J2.
For transducers with an internally installed shunt resistor: 1.) Cal Sense should be attached to the
transducer’s shunt activation connector pin; 2.) External Shunt selected on the Analog Controls;
3.) A shorting wire is to be installed in place of the External Shunt resistor terminals on the rear
of the unit.
( b )
Center the Zero and Span potentiometers as needed by rotating the potentiometers fully CW
(Coarse is 22 turns, Fine is 25 turns), then reverse direction - CCW (Coarse 11 turns and Fine 13
turns) to obtain mid-authority of the controls. Typically this is done on initial calibration. When
recalibrating for minor adjustments this may not be required.
( c )
With mechanical Zero or Balance established at the transducer (transducer “relaxed”); Adjust
Wide Zero then Coarse Zero and then Fine Zero for the Zero position reading on the display or
the desired analog output signal. Display can be adjusted independently to the analog signal.
( d )
Depress and hold the + CAL button while adjusting the Wide Span, Coarse Span and Fine Span
controls, as needed, for precise engineering units reading on the display as determined by the
sensor’s calibration sheet or other reference data (see Equivalent Input shunt calculation below).
( e )
Repeat Steps (d) and (e) to obtain proper measurement readings since the Gain – Span controls
will affect the Zero amplification of the input signal.
( f )
Once completed, if the sensor is going to be utilized in the Negative or CCW mode, depress and
hold the – CAL button and adjust the Symmetry control for a proper symmetrical reading of the
shunt input as noted on the sensor’s calibration data sheet. Note the Symmetry control affects the
Negative Span for approx. ± 2% of full scale adjustment control.
( g )
Release the Cal button and adjust Zero as needed. Re-install the front panel to the instrument.
Minor adjustments and controls are assessable via the front of the unit.
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