where
X
=
Equivalent Input, % of full scale
R
b
=
bridge resistance, ohms
K =
transducer sensitivity, mV/V full scale
R
c
=
calibration resistance, ohms (59 k installed)
Sample Calculation: Assume that K = 3.000 mV/V for a 5000-pound loadcell
(fullscale) with a bridge resistance of 350 ohms.
49.4%
of full scale = 2472 pounds
X =
25000 R
b
K R
c
X =
59000 x 3
25000 x 350
=
If the transducer calibration is unknown, the following calculation is useful to calculate an
Equivalent Input
value for the factory installed, 59K Ohm shunt resistor. This will approximate the value assuming that the
mv/V sensititivity and bridge resistance of the sensor are known.
3. CALIBRATION
(cont.)
Remote Calibration Check:
The instrument can be placed in the calibration mode
(positive or negative) by shorting pin Power Common and SHP for positive or SHN for negative on the
lower I/O connector. Figure 4 indicates two methods of remotely entering the calibration mode
(external switch, or push button control). The Remote Cal function provides a convenient
method of periodically monitoring calibration of the instrument in the positive or negative realm.
Switch 1 - Mode -
current (I) or voltage analog output
Switch 2 - Volts -
+/- 5 or +/- 10 Vdc when mode is voltage
Switch 3 - Current -
4-12-20 or 4-20mA when mode is current
Switch 4 - Filter -
5 kHz or 200 Hz at 3 db, for 200 Hz switch 5 must be down
Switch 5 - Filter -
10 Hz or 200 Hz at 3 db, for 200 Hz switch 4 must be down
Switch 6 - Excitation -
excitaton level, 2.5 or 5.0 Vdc - effects mV/V gain
Switch 7 - Zero Adj. -
extended (100%) or normal (20%) zero authority
Coarse Zero -
16 position switch adjustment for stepped zero balance
control with default calibration indicator.
Fine Zero -
16 turn potentiometer for fine zero balance control
Coarse Span -
16 position switch adjustment for stepped gain contr ol
with default calibration indicator
Fine Span -
16 turn potentiometer for fine gain - span control
Symmetry -
adjust the negative output span to be equal to the positive output
Over Range -
indicates the analog output is 2% greater than mode selected
Power -
indicates the power input voltage is ON
Fig. 2 Front Panel Settings and Indicators
DC Strain Gage Conditoner
Module
IL70A
