Minebea DSA-631, Инструкция по эксплуатации

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29
4-2-2. Bridge box
The bridge box cpmprises a terminal box, a cable and a connector. The terminal box has terminals
for connecting stran gage and contains 3 pieces of high precision resisters (e.g. 120
Ω
for FA410-072).
The bridge circuit is formed by connecting one strain gage or more to the terminals.
(1) Instrallation

Install the bridge box in an area as close to the measurement point as possible.
 The bridge box may be secured with screws using the screw holes shown in Fig. 13, as needed.
 When the bridge box is installed, secure the interconnecting cable, if possible, and connect it to the
amplifier unit.
(2) Connection to bridge box(FA410-072)
A
E
B C D
Bridge Power Supply
Bridge Output
Fig. 4-2 Wire connection on bridge box
 As shown in Fig. 4-2, pins A and C are provided for the bridge power supply, and pins B and D are
provided for the input to the amplifier unit. Pin E is the common terminal.
 This is a bridge for measuring strain. Various methods are used for connecting strain gages. For
details on these connecting methods, refer to “Examples of Strain Gage Bridge Configuration on
page 25 to 27. When using various types of transducers via the bridge box, make connections as
shown in Fig. 4-2.
 If the cable from the bridge box or a transducer to the amplifier unit is long, the bridge voltage will
drop due to the conductor resistance of the cable as shown in Table 4-4. Because the output voltage
from the bridge deviates from the calibration (CAL) value due to the bridge voltage drop, the
calibration value must then be corrected. For information on how to correct it, refer to “Correction of
Calibrated (CAL) Value” on page 33 to 34. The amplifier, however, has (standard ) cable length
correction that provides a proper bridge voltage taking the conductor resistance of the cable into
account. This enables presision measurements without having to pay attention to the difference
between the output voltage and the calibration (CAL) value.
Distance between amplifier and bridge box (m)
Bridge resistance 20 m 50 m 100 m 200 m
60
Ω
-2.4 -5.8 -11.0 -19.9
120
Ω
-1.2 -3.0 -5.8 -11.0
350
Ω
-0.4 -1.1 -2.1 -4.1
500
Ω
-0.3 -0.7 -1.5 -2.9
1 000
Ω
-0.1 -0.4 -0.7 -1.5
Table 4-3 Bridge voltage drop rate (%) (0.5 mm
2
, Wire 20

C)
For information on how to correct the value, refer to “Correction of Calibration (CAL) Value on page
33 to 34.
 Make connections by screwing and soldering.
 If the lead wires from stran gage to the bridge box are long, the gage factor will become apparently
lower and the output linearity will deteriorate, even when the bridge has been initially balanced.
The lead wires, therefore, should be as short as possible (2 m or less). The gage factor of a strain
gage supplied with lead wires attached has been calibrated together with the lead wires. Do not cut
them or add other lead wires.