1. Checkweigher won’t calibrate properly.
| • Not enough test weight on scale. |
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It is recommended that a test weight of at least 50% of your heaviest product run across this scale should be used to calibrate the scale. A weight less than this will not create enough of a difference (span) between no test weight and the applied test weight for the controller to recognize as a valid weight. Keep in mind that the controller’s calibrated operating range is 2 times the size of the test weight. If the unit is calibrated with 5 kg., the controller can only weigh up to a 10 kg. product weight, and then will display an “Over Scale” error.
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| • Too much test weight on scale. |
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The full-load capacity of the scale’s load cell should NOT be exceeded. A test weight that places the load cell into overload will not produce accurate weight readings of your product, and will most likely cause damage to the load cell. Check the capacity of your system before selecting a test weight.
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| • Load cell damage to scale. |
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It is possible for a load cell to receive two types of damage; mechanical overload and shock overload. Mechanical overload, such as applying 20 kg. to a 10 kg. scale, simply distorts the elements within the load cell to a point where they do not return to their previous state, and calibration cannot be done reliably or at all. Shock overload, such as dropping a 5 kg. bag onto the same scale. The 5 kg weight itself is not enough to overload the scale, but the acceleration force of the weight is. Calibration with a damaged load cell will present drift, erratic weights, non-repeatable calibration checks, etc. Load cell replacement is recommended.
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2. Receive an error message in Calibration that says “No Test Weight on Scale / Gain at Min or Max: please contact factory:”
| • Not enough test weight on scale. |
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Check the capacity of your checkweigher first. Use a test weight that is at least 50% of your largest product’s weight for calibration. The controller’s calibrated operating range is 2 times the size of the test weight. If the unit is calibrated with 5 kg., the controller can only weigh up to a 10 kg. product weight, and then will display an “Over Scale” error.
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| • Confirm power supply is working properly. |
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All DC voltages are generated by the 472, and are used to power the 474 Load Cell Digitizer card. If any LED on the front face plate of the #472 card is not lit, remove power from the controller, then remove the 472 card and replace the failed fuse with one of the on-board spares.
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| • Check for 10 VDC output to load cell. |
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Using a digital electrical meter set to VDC, and with the scale controller on, place the leads on the 474 Load Cell Digitizer card terminals 1 and 5. The output should be 10 VDC, plus or minus less than 1%. If the voltage is lower or higher than this value, it may indicate a defective Load Cell Digitizer card or Power Supply card.
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| • Check Load Cell. |
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Using a digital electrical meter set to mV (millivolts), and with the scale controller on, place the leads on the #474 Load Cell Digitizer card terminals 3 and 4. A load cell rated at 2mV/V (total output of 20mV since we excite the load cell with 10 VDC) should have a reading 2 to 12 mV with nothing on the scale (except the weigh station conveyor). The mV reading should increase by about 2 to 4 mV when the test weight is applied.
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A load cell rated at 3mV/V (total output of 30mV since we excite the load cell with 10 VDC) should have a reading of 3 to 20 mV with nothing on the scale (except the weigh station conveyor). The mV reading should increase by about 3 to 5 mV when the test weight is applied.
3. Checkweigher works in Check Calibration mode but doesn’t in the Run Checkweigher mode. What could cause this?
Filter Frequency in the configuration menu has been set to zero (0). Enter the configuration menu, as described in the manual, and confirm this setting. Normally it should be set to 5.
Number of system photo-eyes set incorrectly. Enter the configuration menu, select item #8 (Get Next Menu), then select “P) Photo-Eye Configuration”. This setting should be equal to the actual number of photo-eyes connected to inputs within the controller. If there are no photo-eyes associated with your checkweigher, this value should be zero (0). If there are no photo-eyes, but this value is set to 1 or 2, the checkweigher program is awaiting an input from the photo-eye to trigger termination of the weighment, and will never display a weight value.
4. Inaccurate or non-repeatable weights.
Checkweigher frame installation is critical to proper and repeatable weights. The product entering and leaving the conveyor should be smooth as possible. In-feed and discharge conveyors surrounding the checkweigher should be at the same level and speed. Gaps between conveyors should be kept to a minimum, since too large a gap will allow the product to “nose dive” into the checkweigher, causing product instability.
Support structure for the checkweigher must be isolated and stable. A structure tied to in-feed or out-feed/reject conveyors will induce low-frequency vibrations into the weigh station scale, affecting weight accuracies.
Conveyor belt tension on the Sonic 350, and chain tension on the TSC 350 are very important. Running the belt too tight will cause excessive loading on the conveyor rollers and excessive friction of the belt against the slider bed. The belt should be loose enough to lift at the center between the head and tail rolls, and you should be able to slide your hand between the belt and slider bed, touching the middle of the slider bed. Another way to adjust this tension is to place your heaviest package on the weigh station conveyor and then start the conveyor. The belt needs to be only tight enough to start without slippage of the belt.
Make sure motor cables on the Sonic 350 Checkweigher are not drawn tight, and are anchored properly. Tight or moving cables will cause inaccuracies.
The Sonic 350 conveyor roller bearings must be properly maintained to provide accurate and repeatable weights. If the bearings are worn or have partially failed, the drag and mechanical “noise” generated by the bearing will affect weights.
The head and tail rolls on the weigh station are precision balanced prior to installation. This balance allows the rolls to turn at any speed without generating low-frequency vibrations (kind of like an out-of-balance tire on your car). If the shaft of the roller becomes bent, due to mechanical impact or over-tightened belt, the roller will generate low-frequency “noise” and affect the accuracy of the scale.
The Sonic 350 scale conveyor length and speed have been specifically configured for your application. These two factors, along with your product length, provide Thompson Scale with enough information to formulate the highest possible production rates at the right speed, and provide enough weighment time for each package. However, if the conveyor speed is increased or a new longer package is introduced into production, sufficient weighment time may not be possible. Contact Thompson Scale with information on; maximum product length, conveyor length, and conveyor speed. We will quickly calculate minimum weighment times, and make recommendations on possible solutions to your application problem.
Along with the minimum weigh time, described above, it is also very important that only one product is on the scale at one time. For systems without an exit-end photo-eye (called our Early Weight Terminate photo-eye option), the leading edge of the package must be about 1/4 of its length off the weigh station before we terminate the weighment cycle on that package If the weighment cycle of the first package is not completed prior to entry of another package, weight from the 2nd package will influence the final weight of the first. Make sure that packages are properly spaced.
Load cell damage will also affect weight. The load cell below the weigh station conveyor or weigh table should provide reliable, accurate, and linear weights across the entire weighing surface. Place the controller into the Calibration Check mode, and then place a test weight at the center of the conveyor or weigh table. Record the displayed weight, then move the test weight to each corner of the conveyor or weigh table. The values in each corner should be +/- 2 increments of the center weight value. If one or more corners are out of tolerance, then the load cell or weigh table or conveyor may require adjustment. Contact Thompson Scale to discuss your readings and possible solutions.
5. Weights are always too heavy when compared to a static scale.
The checkweigher controller monitors the load cell output as its only source of weight data. If excessive vibration causes high weight readings to occur while the checkweigher is trying to take a weighment, over-weight values will be generated.
It is possible to enter a TARE or container value in the product setup for each product you run. Make sure that the TARE on the static scale is the same as that of the product setup.
Inaccurate calibration or loss of valid calibration. The checkweigher controller uses values defined in calibration to determine product weights crossing the scale. If this calibration was performed improperly, such as using a 2 kg. weight but entering a 5 lb. test weight value in the controller, the package weights will not be calculated properly. If a significant change occurs to the scale’s load cell, such as overload damage, hitting the weigh station conveyor with a forklift, removing the weigh station conveyor and then replacing, interference from motor or photo-eye connections, it will affect calibration.
Operating Zero can be affected by removing built-up product on the weigh station conveyor and scale. The operating zero is maintained by an automatic zero tracking program within the checkweigher’s program. However, this feature can only zero out a maximum of ˝% of the load cell capacity at one time. If more than ˝% is added or removed at one time, it will be necessary to enter into the Calibration Check screen and manually zero the scale. If this is not done, it may take several package weights to fully re-zero the scale.
Differences in the static scale and the checkweigher’s scale. It is quite possible that the static scale and checkweigher just differ in what is displayed on a package weight. This difference is almost always a small amount, such as 1 or 2 increments different. The static scale may not have the same accuracy or resolution as the checkweigher. If this is the case, it is dangerous to try and compare an accurate scale with one having less accuracy. The static scale should have at least the same accuracy and display resolution as the checkweigher, and best case, should be about 2 times as accurate and the checkweigher.
6. Weights are always too light when compared to a static scale.
Weighment cycle too short.
A package must be on the checkweigher for a minimum period of time to generate an accurate and repeatable weight. Run the package across the scale 10 times, writing down each weight. Are the weights the same, +/-0.5%? If not, most likely there is not enough time for the checkweigher to properly weigh the package. Contact Thompson Scale for further assistance.
It is possible to enter a TARE or container value in the product setup for each product you run. Make sure that the TARE on the static scale is the same as that of the product setup.
Inaccurate calibration or loss of valid calibration. The checkweigher controller uses values defined in calibration to determine product weights crossing the scale. If this calibration was performed improperly, such as using a 2 kg. weight but entering a 5 lb. test weight value in the controller, the package weights will not be calculated properly. If a significant change occurs to the scale’s load cell, such as overload damage, impacting the scale conveyor, removing the conveyor and then replacing incorrectly, interference from motor or photo-eye connections, it will affect calibration.
Operating Zero can be affected by removing built-up product on the scale conveyor and scale. The operating zero is maintained by an automatic zero tracking program within the checkweigher’s program. However, this feature can only zero out a maximum of ˝% of the load cell capacity at one time. If more than ˝% is added or removed at one time, it will be necessary to enter into the Calibration Check screen and manually zero the scale. If this is not done, it may take several package weights to fully re-zero the scale.
Differences in the static scale and the checkweigher’s scale. It is quite possible that the static scale and checkweigher just differ in what is displayed on a package weight. This difference is almost always a small amount, such as 1 or 2 increments different. The static scale may not have the same accuracy or resolution as the checkweigher. If this is the case, it is dangerous to try and compare an accurate scale with one having less accuracy. The static scale should have at least the same accuracy and display resolution as the checkweigher, and best case, should be about 2 times as accurate and the checkweigher.
7. TSC 350 inconsistent weights or no repeatability.
Chain tension is critical to proper weighing. If the tension is too tight, resistance between the chain tension and weigh table will not allow a product to be properly weighed. Too loose chain tension creates problems with consistent transportation of the chain through the chain path, and may cause the drive sprockets to skip teeth.
The flat-top Nylatron© chain used on the TSC 350 has flat side plates that can become chipped, cracked, and worn. Inspect the chain to make sure that both sides and bottom of chain are smooth and defect-free. Replace damaged links.
Proper alignment of the in-feed, weigh table, and out-feed chain guides is critical to accurate and repeatable weighing. Using a taught string or rigid straight edge, confirm that the in-feed and out-feed guides are straight and parallel to the weigh table.
In-feed and out-feed chain guides must be at the same height as the weigh table. Using something similar to a business card, slide the edge of the card along the in-feed guide, and across the weigh table. The card should slide smoothly across these surfaces. If bumps or drops are felt, level the guide
The TSC 350 is provided with replaceable end caps on the in-feed and out-feed chain guides. This is the highest wear part of the chain path, and once work, the end caps can be a source of mechanical noise and chain surge.
Some TSC 350 Checkweighers are provided with a Early Weight Terminate photo-eye at the discharge end of the weigh table. This photo-eye must be aligned to catch the leading edge of the product at the instant the product is transferring from the weigh table to the out-feed guides. Adjust the photo-eye as necessary.
8. The reset light on the 470 CPU/ 476-interface card flashes.
This LED is provided as a “heartbeat” indicator. As long as the LED blinks on and off at a steady pace, the controller’s CPU is operating properly. If this LED is continuously ON or OFF, consult the factory for more in-depth trouble shooting assistance.
9. A feature/setting previously used is not working or is operating differently.
If an updated program EPROM was installed into your controller it is possible that a feature has been moved or modified as part of the updated program. Contact us for more information on your specific program.
10. Password problems.
Password is required, but either don’t know it or don’t have one.
Press front panel ESC key until display shows Main Menu. Now select item 5 (Select/Edit Product), then 3 (Edit Password). When asked for password, type in the word “scale”. The next prompt will be for entry of a new password. If desired, enter a new password. To disable password protection, press the Space Bar once, then press Enter.
11. Keyboard keys not working properly.
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.
12. Why does my Checkweigher lock up (freeze or blank out) from time to time?
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.
13. Reject conveyor/device won’t operate properly.
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.
14. Outputs 1, 2, & 3 are flashing (checkweigher only) What does this tell me?
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.
15. Lines on LCD display screen.
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.
16. Why does the screen flicker/flash?
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.
17. Display is dim or too bright and washed out.
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.
18. Sonic 350 conveyor belt stalls.
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.
19. Sonic 350 belt race condition.
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.
20. Belt(s) off, but switch in “run”
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.
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Heavy Duty Checkweighers 
