Minebea DSA-631, Instruction Manual

Page: 44 / 64

34
(2) Where bridge configurations are not quarter bridge configuration
The calibration (CAL) values of this amplifier unit are equivalent voltage values based on the 2.00
gage factor and the quarter bridge configuration. The calibration values based on half or full bridge
configuratins can thus be obtained by referring to the next table.
The relationship between the bridge supply voltage and bridge output voltage can be represented
bythe following formula.
e = (K
x ε x
E x Bridge configuration) / 4
Where : K : gage factor,
ε
= Amount of strain (10
-6
strain), E : Bridge voltage
Method True calibratin value
Tow gage
One active one dummy Calibrated value on display
x
1
Two active Calibrated value on display
x
1/2
Opposite arm, two active Calibrated value on display
x
1/2
Four gage Four active
Calibrated value on display
x
1/4
Transducer Four active Calibrated value on display
x
1 (*)
Table 4-6
For details, refer to the remarks in the “Wheatstone Bridge Connectin Table” on pages 26 to 27.
* Although transducers are generally based on the full bridge configuration, their output is made
tomatch the quarter bridge configuration.
(3) Where the distance from the bridge box to the amplifier unit is long
If the cable from the bridge box or a transducer to the amplifier unit is long, the bridge supply will
drop due to the conductor resistance of the cable. This causes errors between the bridge output
voltage and the CAL value. For obtaining the voltage drop rate, refer to “ Bridge Voltage Drop Rate”
on page 29 or measure the voltage drop rate between terminals A and C on the bridge box, using a
voltmeter.
Example :
If the cable length is 100 m and the strain gage resistance is 120
Ω
under an ambient temperature
of 20  C, the bridge supply voltage will be reduced by 5.8 % between terminals A and C, which can
be obtained from the “Bridge Voltage Drop Rate Table” on page 29. The true calibration value can
thus be given by :
True calibration value
=
x
Calibration value on display
Such measurement and adjustment are not needed in DSA-631 amplifier thanks to cable
length compensation (refer to page 17 to 18.)
1
1 – 0.058
A
E
B C D
Voltmeter
AC voltage
Measurement
Bridge box
Fig. 4-7 Voltage measurement on bridge box