OHAUS FD SERIES Service Manual

Also see for FD Series: Instruction manual User guide Quick start guide

Contents

OHAUS FD SERIES Service Manual Manual pdf 18 page image

3-2CHAPTER 3 SCALE TESTING AND CALIBRATION3.3 TESTING THE LOAD CELL ASSEMBLYThis section contains three methods of testing the Load cell.3.3.1 Ramp TestRefer to Appendix A and perform the Ramp Test. If the Ramp Test passes, continue with the rest of thisprocedure.3.3.2 Resistance Test1. Refer to Section 4.1 and remove the Top Housing.2. Remove the Load Cell cable connector from J1 on the Main PC Board. Using an Ohmmeter,measure in accordance with Table 3-1 Load Cell Resistance Readings on the cable. If theresistance readings vary more than the table readings allow, replace the Load Cell in accordancewith the procedure in Section 4.4. This resistance test is useful in determining if the Load Cell hasbeen severely damaged by a short or open circuit which has occurred on the cell or wiring. If theLoad Cell resistance readings are good, continue with this procedure.TABLE 3-1 LOAD CELL RESISTANCE READINGSMEASUREMENT POINTS READINGPins 1 & 4 408 + 10 OhmsPins 2 & 3 350 + 4 OhmsNOTE: Pins 1, 2, 3, and 4 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.3. Reconnect Load cell cable to J1.3.3.3 Excitation and Output Voltage TestNOTES: 1. The following steps involve power applied to the scale.2. Solder contacts located above connector J1 can be used as measuring points. See Figure 3-2.1. Insert the 4 Pan Support Caps into the Load Cell Frame and place the Pan on top.2. Turn on power to the scale by momentarily connecting pin 1 and 5 on J2.3. With no load on the Pan, first measure the excitation voltage across pins 1 and 4 of J1 on the PCB.This voltage must be 5.0 Volts dc with the Load cell connected. If the voltage is lower, disconnectthe Load Cell cable from the PC Board and measure again. If the voltage is 5 Volts dc, the LoadCell is defective and must be replaced. If the voltage remains low, the regulated 5 volt powersupply on the PC Board is defective and the Main PC Board must be replaced. For Main PC Boardreplacement, see Section 4.3.