Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/772143
AGGREGATES MANAGER / January 2017 35 rod coming into the building. The multi-meter should read less than 1 ohm. Measure the AC voltage across the ground and neutral of the AC outlet. The result should be 0 volts AC, not to exceed 0.5 volts AC. Fol- lowing both of these procedures is recommended; however, completing one of the steps above should allow you to evaluate the quality of the ground. If you discover grounding issues with the AC power supply, notify the building owner and/or the power company. 2. Check the scale's grounding. a. Make sure the scale and all peripherals are connected to a transient protection device such as an uninterruptible power sup- ply to deter voltage distortions. b. Use a bare, 10-gauge copper wire connected to the frame of the scale platform and the grounding lug on the junction box board, and run the copper wire back to the ground rod provided by the power com- pany. The copper wire can be buried underground from the scale to the AC ground. c. If your scale uses transient pro- tection such as an uninterrupt- ible power supply, the device needs to be grounded to this wire as well. d. Make sure a braided transient bypass cable is positioned across each load cell mount to ensure electrical transients pass through the bypass cable instead of the load. e. Measure the resistance between the scale sections and the AC ground. The reading should be less than 1 ohm. Higher readings are typically caused by corroded connections. f. Check the AC power supplied to peripherals such as remote dis- plays, printers, and computers. A remote device may not have the same AC power source as the indicator; therefore, each device may not be grounded to the same point. Transient protection devices should be grounded to the same wire as the peripher- als they are protecting. g. Measure the resistance between the AC power ground-points. The multi-meter should read less than 1 ohm. Calibration and testing Truck scales should be calibrated and tested by a state-licensed service agency using no less than 12.5 percent of the scale's nominal capacity, or 25,000 pounds of certified test weights. The scale's calibration interval is determined by the frequency of use, individual appli- cation requirements, and federal, state, and local guidelines. Each section of the scale should be tested and detailed test reports should be provided to the cus- tomer and government authorities. Truck scales are traditionally long- term investments that should provide de- cades of reliable and dependable service. Saving a few hundred dollars on the front end may cost thousands in unexpected maintenance costs later. With proper maintenance and grounding, aggregate producers can extend the life of their truck scales and keep their "cash register" fully operational. AM Article courtesy of Rice Lake Weighing Systems. Keep your scale clean and dry. Be sure to remove all debris. Truck scales should be calibrated and tested by a state-licensed service agency using at least 12.5 percent of the scale's nominal capacity.