Measurement Computing WBK Options - Manual (Page 73)

WBK16, Strain-Gage Module 949794 WBK16, pg. 33
The External Shunt Calibration method requires that the user enter the following 5 parameters:
Excitation - The value of the constant voltage source used to excite the gage.
Max Load - The maximum load value that the gage is expected to measure. This value could be less than
the max rated load of the gage.
Quiescent Load - The minimum load value that the gage is expected to measure. This value could be
greater than the minimum rated load of the gage.
Point 1 Units - The user-supplied, at rest value of the load applied to the gage. If no load is applied to the
gage in its quiescent state, enter “0”zero.
Point 2 Units - The user-supplied effective load value that will appear at the gage when the external shunt
resistor is switched into place. This load value must be calculated based on the value of the
external shunt resistor.
As with the Internal Shunt method, calibration accuracy is directly tied to the accuracy and stability of the shunt
resistor used.
Name Plate Calibration
Name Plate Calibration is similar to the 2 Point Auto Calibration method. No actual measurements are taken
during the calibration process. The calibration constants are calculated from information provided by the user. The
method is called “Name Plate” because the calibration information is obtained from the Name Plate or Label that is
attached to the gage or load cell.
The Name Plate Calibration method requires that the user enter the following 5 parameters:
Excitation - The value of the constant voltage source used to excite the gage.
Sensitivity - The output of the gage measured in millivolts per volt.
Full Rated Load - The maximum rated load of the gage.
Max Load - The maximum load value that the gage will be expected to measure. This value could be less
than the max rated load of the gage.
Quiescent Load -The minimum or at rest value of the load applied to the gage. If no load is applied to the
gage in its quiescent state, enter zero. WaveView assumes the Min Load value is equal to the
quiescent load value.
Calibration Example using the Name Plate Method and a Load Cell
The following example uses Name Plate calibration with a load cell.
Load cells come with a mV/V specification (frequently referred to as sensitivity) which means for each volt
of excitation at maximum load, the load cell will output a specific millivolt level.
Consider a 3000-pound load cell rated at 3 mV/V using 10 V of excitation. When the load cell is used,
a 10-pound platform will be placed on it. Although the load cell is rated at 3000 pounds, 1500 pounds is
the maximum load that will ever be applied for this example.
From the above data we know the following parameters:
• Excitation Voltage = 10 volts
• Maximum Applied Load = 1500 pounds
• Quiescent Tare = 10 pounds
• Sensitivity = 3 mV/V
• Full Rated Load = 3000 pounds
Note: These 5 values are used in the following figure.