OHAUS EC SERIES Service Manual

Also see for EC Series: Instruction manual Instruction manual

Contents

OHAUS EC SERIES Service Manual Manual pdf 16 page image

3-2CHAPTER 3 SCALE TESTING AND CALIBRATION3.3 TESTING THE LOAD CELL ASSEMBLYThis section contains two methods of testing the Load cell.3.3.1 Resistance Test1. Refer to Section 4.1 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 accordancewith Table 3-2 Load Cell Resistance Readings on the cable. If the resistance readings vary morethan the table readings allow, replace the Load Cell in accordance with the procedure in Section4.4 or 4.5. This resistance test is useful in determining if the Load Cell has been severely damagedby a short or open circuit which has occurred on the cell or wiring. If the Load Cell resistancereadings are good, continue with this procedure.TABLE 3-2 LOAD CELL RESISTANCE READINGSMEASUREMENT POINTS READINGWires 2 & 5 415 + 15 OhmsWires 3 & 4 350 + 3 OhmsNOTE: Wires 2, 3, 4 and 5 must be isolated from chassis ground and shield. Resistance should begreater than 5 megohms. A lower reading indicates a short in either in the Load Cell cable or the LoadCell.4. Reconnect Load cell cable to the Main PCB.3.3.2 Excitation and Output Voltage TestNOTES: 1. The following steps involve power applied to the scale.2. Load Cell solder contacts can be used as measuring points. See Figure 3-2.1. 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 Cellconnection on the PCB. This voltage must be 5.0 Volts dc with the Load cell connected. If thevoltage is lower, disconnect the Load Cell cable from the PC Board and measure again. If thevoltage 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 Boardreplacement, see Section 4.3.