Omega Engineering OMB-DBK-34A, User Manual

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10. Return the physical calibration switches (of the applicable DBK43As) to the NORM position.
11. In LogView, open the LogBook Hardware Configuration Window (hardware tree) and select NORM
for each DBK43A.
This completes the section entitled: “Procedures Common to All Calibration Steps (Required)”
Nameplate Calibration and Manual Calibration
To properly calibrate a strain gage channel using the Nameplate method , the required gain must first be
calculated. If the desired gain and offset are already know [as in the Manual calibration method] skip to
the section, Determining the Gain of Each Amplification Stage .
The following examples outline the necessary steps for determining the required gain for
Nameplate calibration . Both strain gage and load cell examples are provided.
Calculating the Required Gain
Determining a Strain Gage’s Maximum Output Voltage
Most strain gages come with Gage Factors (GF) used to calculate the approximate output of the bridge
circuit with a typical strain value. The formula is:
V
BR
= (V
EXC
* G * S * B) / 4 [See following important notice]
Where: V
BR
= Bridge output voltage
V
EXC
= Excitation Voltage
G = Gage Factor
S = Strain in user units (in uStrain)
B = Configuration factor (1 for ¼ bridge, 2 for ½ bridge, 4 for full bridge)
The equation, V
BR
= (V
EXC
* G * S * B) / 4 produces a linear estimate. If you are
using a non-linear strain gage you should refer to strain gage theory for additional
information as needed.
For a 120 ohm strain gage with a gage factor of 2.1 and excitation voltage of 5 V, applying
4000 microstrain would produce an bridge output of 10.5mV for a ¼ bridge configuration.
V
BR
= (5 * 2.1 * 4000x10
-6
) / 4 = 10.5mV
Determining a Load Cell’s Maximum Output Voltage
Load cells come with a mV/V specification—for each volt of excitation at maximum load, the load cell
will output a specific millivolt level.
V
LC
= R * V
EXC
Where: V
LC
= Load cell output voltage
R = Load cell spec (mv/V)
V
EXC
= Excitation voltage
DBK16, pg. 20
879895
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