OHAUS EB SERIES, Руководство по обслуживанию

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CHAPTER 2 DIAGNOSIS
EB Series Scales Series Service Manual 2-7 Ohaus Corporation www.ohaus.com
2.7 TESTING THE LOAD CELL ASSEMBLY
This section contains two methods of testing the Load cell.
2.7.1 Resistance Test
1. Refer to Section 3.1 and remove the Top Housing.
2. Refer to Figure 3-2 and record color code and position of the wires from the Load
Cell.
3. Unsolder the Load Cell cable from the Main PC Board. Using an Ohmmeter,
measure in accordance with Table 2-9 Load Cell Resistance Readings on the cable.
If the resistance readings vary more than the table readings allow, replace the Load
Cell in accordance with the procedure in Section 3.4 or 3.5. This resistance test is
useful in determining if the Load Cell has been severely damaged by a short or open
circuit which has occurred on the cell or wiring. If the Load Cell resistance readings
are good, continue with this procedure.
TABLE 2-9. LOAD CELL RESISTANCE READING.
MEASUREMENT POINTS READING
WIRES 2 & 5 415 ± 15 Ohms
WIRES 3 & 4 350 ± 3 Ohms
NOTE : Wires 2, 3, 4 and 5 must be isolated from chassis ground and shield.
Resistance should be greater than 5 megohms. A lower reading indicates a short in
either in the Load Cell cable or the Load Cell.
4. Reconnect Load cell cable to the Main PCB.
2.7.2 Excitation and Output Voltage Test
Notes:
– The following steps involve power applied to the scale.
– Load Cell solder contacts can be used as measuring points. See Figure 2-2.
1. Insert the Pan Support into the Load Cell Frame and place the Pan on top.
2. Turn on power to the scale.
3. With no load on the Pan, first measure the excitation voltage across point 2 and 5
Load Cell connection on the PCB. This voltage must be 5.0 Volts dc with the Load
cell connected. If the voltage is lower, disconnect the Load Cell cable from the PC
Board and measure again. If the voltage is 5 Volts dc, the Load Cell is defective and
must be replaced. If the voltage remains low, the PC Board is defective and the Main
PC Board must be replaced. For Main PC Board replacement, see Section 4.3.
4. Refer to Figure 2-2 and measure the voltages on points 3 and 4, +SIG and
–SIG
points. These measurements represent the output of the Load Cell. Repeat
measurements at 50% and full scale capacities. See Table 2-10 for typical readings.