Scenario: Your Ludlum Model 329-Series laundry monitor has been functioning properly, and then one day the count display fails to update or is purely erratic. The operator also complains of static discharge problems when the conveyor belt is touched.
What's the Grounding Strip For Anyway?
Within the past couple of months, these problems have been encountered by some of our laundry monitor customers. Most of the time the problem described is with the ground connection between the conveyor belt and chassis ground. If the ground connection to the belt is defective or missing, the metal belts friction against the polyethylene table can develop an extreme static charge. As this charge continues to build and finally discharges to something or someone, a static discharge is produced. This excessive discharge can damage the sensitive microprocessor control electronics within the electronics console. For the model 329-1-Series monitor, this grounding strip consists of a phosphor bronze strip approximately 3⁄4 inch wide by 3 inches long which rides against the upper conveyor belt. This strip must be replaced periodically to ensure a sufficient ground connection because of belt wear upon the strip. The bottom belt ground is actuated by the contact of the conveyor belt to the detector protective cover. However, some of the original protective hex covers have been replaced with a brass cover which has a layer of UHMW polyethylene on them. To ground the conveyor belt on these units, a split blank sprocket (LMI # 7323-974) should be mounted on the drive shaft which will provide chassis ground through the conveyor drive motor. This sprocket can be mounted without removal of the conveyor belt.
The Model 329-32 upper conveyor belt utilizes a stainless steel blank sprocket to provide the ground connection between the belt and the drive shaft. A brass strip is then connected from the end of the drive shaft to the chassis to complete the ground connection. The bottom belt also uses a stainless steel blank sprocket to make the connection from the belt to the drive shaft but the ground connection is completed through the conveyor drive motor via the chain.
If a static problem is occurring, inspect the ground connections described above. Use an ohmmeter to verify continuity between the conveyor belt and chassis ground. If you have questions about this or other LMI products, please contact the LMI Repar Department.
From March 1993 Newsletter