Frequently Asked Questions - Small Package Checkweigher FAQs

The keyboard provided on the 4693 controller is read by the #476 card located at the bottom inside of the controller door. In the bottom left corner of the 476 card are two (2) red LED’s. One is dedicated to the processor chip on this card, and blinks on/off like a heartbeat to show proper operation of the processor. The other LED provides a visual indication that a key press on the keyboard is properly read. Press the suspect key(s) while watching this LED. If the LED does not blink each time the key is pressed, the key has most likely failed. If the LED does blink, but the controller does not properly respond, the 476 card may be defective. Contact Thompson Scale for further assistance and to purchase replacement parts required.

The 4693 controller is provided with a switching power supply input for source 110 VAC power. This power supply does an excellent job of filtering “noise” and voltage/frequency variations in the source 110 power. However, it cannot filter out everything. It is possible that your source 110 VAC supply to the controller is subject to surges, spikes, sags, etc. that are more prominent than normal. Check the source power, and possibly install a line conditioner to see if this eliminates the problem. Call Thompson Scale for a recommendation on line conditioners.

EMI/RFI from Inductive loads. A device such as a solenoid valve coil or relay coil, or transformer style pilot light, are all considered as inductive devices. When the coil of this device is energized via one of the checkweigher’s outputs, a magnetic field is created around this coil. When the device is de-energized, this field collapses, causing a momentary current inrush to occur. This inrush current can feed back to the output that originally turned on the device, and in extreme cases, can cause the controller to reset. Install a snubber (quench arc) across the COIL of the device. This should eliminate the problem. Contact Thompson Scale for recommendations on snubbers and their proper installation.

Static discharge is another possible source of this problem. Make sure that a proper ground has been attached to the weigh station conveyor (make sure it’s loose enough not to interfere with weighing) and controller. Static build-up on the conveyor belt is kept to a minimum by use of our standard anti-static belting.

The reject output is operated by one of two outputs within the checkweigher controller. First, it is important to determine the reject configuration for your application. It is possible to have an input from a metal detector, providing timed reject output, and a reject for low weight, high weight, and metal contaminated product. The configuration for these rejects can be found in the configuration menu. Please reference your user’s manual for instructions on how to find and configure this variable.

Timers are provided in the checkweigher controller; Main Menu item #4 “Set Time, Date, Reject Time”. A setting for a reject delay (time it takes for the rejected package to reach the reject device), and reject duration (time required to actuate the device). If the reject duration is set to 0.0, the reject output will NOT come on.

Checkweighers with reject devices operated by other controls (system motor controls, etc) most likely require only a pulse reject output to the external controls, with the external controls providing the timing functions. In these cases, the reject delay should be set to 0.0, and the reject duration to approximately 0.3 second

If the reject device is operated via the checkweigher controller directly, and packages are not reliably discharged from the reject, it is possible that the #473 I/O card in the controller is experiencing problems. Replace this card to confirm. The reject device itself may also be experiencing problems, with too low air pressure, a sticking or erratically operating solenoid valve, or an air cylinder that has a bad seal or sticky shaft. Check and confirm proper operation of each of these components.

If the Early Weight Terminate photo-eye at the discharge end of the weigh station conveyor has become blocked for more than 15 seconds, an alarm is triggered, turning on these three outputs. This can be caused by mis-aligned or dirty photo-eyes, or a production line stoppage that has placed a container in front of this photo-eye.

The LCD display module is composed of several components, including a conductive rubberized strip that lies between the LCD circuit board and the LCD glass. If corrosion or product contamination gets into this area, it can cause a loss of continuity between the strip and glass, presenting a blank (off state) line on the display. Due to the precise orientation of the strip to glass, it is not practical to disassemble and clean this area since proper re-assembly is extremely difficult.

The LCD should be replaced, and care should be taken to ensure product dusts or gasses do not enter the enclosure.

The 4693 checkweigher or filler controller includes a hard display reset that invoked every 15 seconds. This reset re-writes the display screen from top to bottom, and the flicker or flash seen is the very fast moving re-write line as it moves down the screen.

The LCD graphics module uses a fluorescent back light provided with an adjustment for contrast. Over time, the back light may loose some efficiency and require adjustment. Open the controller door and locate the #476 card at the bottom of the door. In the upper left corner of the 476 card is a daughter card with a connection of two white wires to the display’s back light. Just to the right of this daughter card is a small blue potentiometer with a white center. This is the contrast adjustment. Adjust as necessary. If this does not resolve the problem, contact Thompson Scale for further assistance.

Too heavy product crossing the scale, causing the conveyor motor to overload and stall. Can also be caused by products being too close together, with more than one package on a conveyor at one time.

Failure of the conveyor motor. Although unlikely, the motor can become damaged by excessive loads or missue. Replace motor and return to factory for testing.

Belt tension too tight, causing high friction with slider bed and bearings. Belt tension should be only tight enough to reliably transport packages across the conveyor. Loosen the belt, apply the heaviest package to the center of the conveyor, and then turn the conveyor on. The conveyor should start and the package move across the conveyor without any belt slippage.

Product build-up between belt, bearings, and bed. Clean conveyor and return to service.

Interlock to up/down stream conveyors may intermittently start and stop the checkweigher as part of overall line traffic control.

Conveyor under too much load, stalling conveyor. The Sonic 350 conveyors use servo motors that are instructed to run to a certain “infinite” count. When the motor stalls and then is again able to run, the motor programming requires that the servo catch up to the supposed current count value. This causes the motor to race for a second or so until it has caught up, then returns to the proper operating speed.

Loss of communication with the controller’s #477 card. This card sends instructions to each motor, in return receiving an acknowledgment from the motor. Replace this card and test again.

Blown motor fuse. Each motor is protected by an individual 3AG 1 Amp glass fuse, found on the motor control panel next to the switching power supply. Check fuses.

Motor speed set to zero (0), or motor parameter settings changed. Motor speed can be set in the configuration menu. Along with this speed setting are settings for acceleration, deceleration, and other important motor parameters. Check user’s manual for further information on these settings.