Measurement-computing DBK Part 2 Manual do Utilizador descarregar pdf (Página 50)

DBK43A & DBK43B, pg. 30 899892 DBK Option Cards and Modules

11. DBK43A users: In LogView, open the LogBook Hardware Configuration Window (hardware

tree) and select NORM for each DBK43A.

DBK43B users

: In LogView, open the LogBook Hardware Configuration Window (hardware

tree) and select RUN for the CAL1 switch and select CAL for CAL2.

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

EXC

* G * S * B) / 4 [See following important notice.]

Where:

= Bridge output voltage

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

= (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.

= (5 * 2.1 * 4000x10

-6

) / 4 = 10.5 mV

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.

= R * V

EXC

Where: V

= Load cell output voltage

R = Load cell spec (mv/V)

EXC

= Excitation voltage

Consider a 3000 pound load cell rated at 2.05 mV/V using 10 V of excitation (assume a 350Ω load cell).

When 3000 pounds is applied, the voltage out of the load cell is 20.5mV.

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