DayTronic IL78A Manual - Página 12

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3. CALIBRATION

With the transducer loaded as in step (f), adjust the Symmetry control (right above the PHASE

(j)

control adjustment) to obtain a dead weight reading equal to that obtained in step (f).

If dead weight calibration is not practical and the transducer manufacturer has supplied a

(k)

calibration resistor (or resistor value), install the recommended calibration resistor. See

Fig. 5

Perfom steps (b) thru (e). Now activate the SHUNT POSITIVE (SHP) terminal

(l)

and adjust the SPAN controls until the instrument output is equal to the Equivalent Input

value simulated by the installed resistor. Shunt is performed at zero load.

If a negative Equivalent Input value is also provided on the calibration sheet of the transducer

(m)

under calibration, activate the SHUNT NEGATIVE (SHN) terminal. Confirm that the negative

value can also be obtained. If necessary, adust the SYMMETRY control to obtain the negative

Equivalent Input value as listed on the calibration document. The SYMMETRY control has

approximately 7% authority, full scale.

If dead weight calibration is not practical and the transducer calibration data is unknown,

the Equivalent Input value for the factory-installed calibration resistor can be

approximated as follows, assuming that the mv/v sensitivity rating of the transducer

and the bridge resistance are known.

where

Sample Calculation: Assume that K = 3.000 mV/V for a 5000-pound load cell

(fullscale) with a bridge resistance of 350 ohms.

Note: Above calculation is useful in applications involving non - star bridge shunt calibration strain gage bridges (for

example DC bridges, and slip ring type torque sensors). Rotary transformer type sensors which use star bridge shunt

circuit will not equate properly and the sensor's published calibration data should be referenced.

AC Strain Gage Conditioner Module

(cont.)

25000 R

X =

K R

X =

Equivalent Input, % of full scale

bridge resistance, ohms

K =

transducer sensitivity, mV/V full scale

calibration resistance, ohms (59 k installed)

25000 x 350

X =

59000 x 3

49.4%

of full scale = 2472 pounds

IL78A

Calibration IL78A.3