Model 3770
DC STRAIN GAGE PANEL METER
4.
CALIBRATION
This section contains the instructions for calibrating the 3770. Included is a functional description of the instrument
front-panel (see Page 1). To perform calibration, proceed as follows.
( a )
Connect Sensor and Analog terminals as required. Connect and apply power to the unit. 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 cover of the
3770 unit by removing the two small Phillips screws on the front panel. TARE should not be
activated.
( b )
Center the Zero and Fine Span potentiometers by rotating the potentiometers CW until you feel the
“end stop” or by the number of turns accomplished (Coarse is 22 turn, Fine is 25 turn). Rotate the
potentiometer back to the middle of their range (Coarse 11 turns, Fine 12-13 turns). This will
establish the adjustments middle authority.
( c )
Position the front panel switches to the desired settings for the application. Refer to Section 3 for
details.
( d )
Relax the sensor input to “zero” load and adjust the Wide Zero and Fine Zero controls until the
meter reading is achieved at the point which will be the “zero” value reference.
( e )
Once the Zero position has been established, apply a known load typically in the nominal working
range of the sensor. With the load active and stabilized, adjust the Wide Span, Coarse Span and
Fine Span controls until the display reading required is achieved.
( f )
Return the sensor to the "Zero" position and re-adjust the Coarse Zero and Fine Zero controls for
the desired reading or analog output of the unit. Repeat the Span (step e) adjustment as necessary to
achieve the proper reading or analog output. Note that changes in Span (Gain) will affect Zero.
Span and Zero re-adjustments may need to be repeated to obtain the desired reading. (Note that the
3770 meter also has independent display adjustment capability to where the digital display can be
adjusted independently to the analog output signal of the unit so as to achieve proper analog output
levels from the meter.)
( g )
Once the Zero and the Gain (SPAN) adjustments have been accomplished, if needed - the user can
adjust for Negative non-symmetrical value (as referenced by the positive SPAN value) by utilizing
the front panel Symmetry control when the load is Negative. To accomplish this, apply a known
negative load and adjust the symmetry control for the correct readout or analog output signal
required. Note the Symmetry control has approx. ± 2 % full scale authority.
( h )
Once completed, replace the front display lens cover to the original position and ensure proper shielding and
grounding have been done to the meter. Minor calibration adjustment may be accomplished using the front
panel potentiometer for zero and span.
Display Calibration
The 3770 instrument display has separate adjustment controls that are independent of the
analog output controls - allowing the user to alter the display reading to a value that is suited for the display while
maximizing the analog output amplitude. In the standard – default switch position (as marked near the Coarse
Display Span control), the display has a fixed full scale reading set by the display range switches of 5000, 10000 or
20000 counts. At theses settings the full scale analog output signal will be 5 Vdc or 10 Vdc, as selected via the
analog controls. To accomplish the display adjustment change, the user would first set the desired display range
and decimal location using the display dip switches, adjust the analog output to the desired level and then adjust the
display Coarse then Fine span controls for the required digital readout.
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