Both messages mean the processor has lost its digital link to the scale card at the weigh frame, so load, speed and scale status have all stopped arriving and nothing the scale shows or sends can be trusted. Scale data error is the WP20 and WP25 wording; bad scale card comms is the WP50’s. It’s far more often the cable, a gland, a terminal or a link left out after a board change than a dead board.
We’re an independent service company, not a Tecweigh dealer or agent. For bookings and parts, see Tecweigh belt weigher and WP-series servicing. For the other messages, see what the messages on a Tecweigh WP50 mean and Tecweigh WP20 and WP25 fault codes and calibration.
What does the message actually mean?
The load cells and speed sensor wire to a scale card at the weigh frame, which sends the result back over one digital link. Break that link and you lose everything at once: the rate goes to nothing, the total stops, and whatever goes to the plant has nothing behind it. Because speed rides the same link, a Tecweigh showing no speed may have this fault rather than a sensor fault.
Don’t calibrate while it’s showing: there’s no trustworthy load or speed to calibrate against, and the manual blocks it anyway.
| Message | What we check first | When to call us |
|---|---|---|
| Scale data error (WP20, WP25) or bad scale card comms (WP50) | The indicators at both ends, then the cable, glands and terminals. Has a board been changed recently? | If the cable and terminals look sound and it’s still down, or it comes and goes. |
| Low scale power (WP50) | The voltage at the scale card against the threshold for that card type. Measure at the frame, not at the processor. | If the supply at the frame checks out. |
| Low power (WP20, WP25; LOW POWER on the WP50) | What has been added to the scale supply since commissioning, then the incoming supply, the run length and the cable. | If the supply, cable and added loads check out. |
Does the wording tell you which Tecweigh you have?
Usually, and the boards settle it: the WP20 is built on an MP400, the WP25 on an MP600, and the WP50 on an MP800 main board with a DI400 display board, so a photo of the board inside helps us bring the right parts.
A WP25 can be wired direct to the processor or through a scale card. Scale data error and low power only exist in scale card mode, and in that mode its serial port is dedicated to the scale card, so it can’t also serve the plant. The WP50 always uses a scale card.
Why does the same cable run sometimes show low power instead?
One says the link is broken, the other says the scale card isn’t getting enough supply, and both live on the same cable run. We don’t print a voltage: the WP50 gives a different threshold for each of three scale card generations, and the Australian WP20 manual gives two different minimum supply figures in two places. Measure at the scale card terminals, against the document for the card fitted.
The WP50’s older style LOW POWER message lists: incoming supply below the minimum for the AC or DC version, the processor not producing its rail, a run longer than about 1,200 m, attached devices such as a chart recorder drawing more than 1 A in total, or a break or short in the cable. The added load is the one we most often find.
On a displacement carriage with the replacement scale card, a small link sets whether the card monitors its own DC supply; with it off, you get low power on a good supply. It’s in that card’s addendum.
What can your site check first?
Work on or near a conveyor, or inside an electrical enclosure, needs isolation under your site’s procedures and trained, authorised people. If that’s not you, stop and call us on 1300 101 666.
- Write down the exact wording and the time it first appeared. That’s the window of tonnes you’ll need to account for.
- List what’s been added to the scale supply since commissioning.
- Ask whether anyone has worked on it. A swapped card still set for another system, or a termination link in the wrong place, both cause this fault and both survive a visual check.
- Look for the obvious on the way past: a damaged gland, water in an enclosure, a cable pulled tight by something that has moved.
What order do we work through it in?
Each step rules out half of what’s left:
- Indicators at both ends. On a WP50 the scale card’s comms indicator flashes about five times a second while it’s being asked for data, and the main board has send and receive indicators by the scale connector. On older boards, green at the scale card means adequate supply, red means insufficient supply or a failed board, and a yellow indicator pulses about five times a second while comms are healthy.
- The cable: walk the run for damage, then prove continuity end to end and no shorts between conductors.
- Live volts at the terminals, everything connected and powered.
- Resistance at the same terminals with the power off. The most skipped step, and the one that tells you the most.
- Unplug the link and measure each board separately. That’s what decides between replacing a board and replacing a cable.
That sequence is the WP50’s; the WP20 manuals have their own. The cause lists differ too. The Australian WP20 lists the two data conductors reversed, no supply rail from the processor, a run over about 1,200 m, and a break or short. The US edition adds an address switch left on, surge damage to either board and a blown main board fuse. The WP25 adds a termination link in the wrong position. We don’t print terminal numbers or expected readings: they differ by board and generation.
Why do the termination links have to be right first?
The WP50 procedure assumes the termination links are fitted on both the main board and the scale card. If one is out or in the wrong place, every reading is compared against the wrong expectation, and a good board gets condemned. We don’t print link positions, because they differ between manual generations and most of the installed base is older than the current book. In our experience it’s the cause most often missed after a board swap.
Is this what a lightning strike looks like?
Often. Resistance well below what the document expects usually means a surge suppressor on a board has taken a hit, while the cable tests fine, so replacing the home run first wastes the shift. Look at both boards for burnt components, then split the link and measure each board to find the damaged end.
For prevention, the WP20 manual asks for individually and overall shielded instrument cable to the scale card with the shields landed at the processor end only, the run kept away from noise sources, and no welding on or near the scale. See protecting belt weigher electronics.
Can you see it coming?
On a WP50, yes. The maintenance menu shows the scale comm errors count: errors in the data from the scale over the last minute. A healthy hard wired link sits at zero. A count that climbs visit on visit is a cable failing, which makes it a planned repair instead of an outage. We record it against the asset in AIMM, our asset management system.
The count is also published over the comms card, and a WP50 relay set to the error function operates on a scale data error, a load error or low power. See getting Tecweigh WP50 faults into the PLC.
If the link is healthy and the numbers are simply wrong, start at is it the load cell, the cable or the junction box? We keep the settings of the scales we look after, so a replaced board is a reload and a proving run, not a recommission.
We supply parts for Tecweigh and the other major belt weigher brands: a genuine part where it’s available, or a suitable alternative, with compatibility confirmed and the part identified on the quote.
Need a manual for your equipment?
On a displacement carriage you may also need the short addendum for the replacement scale card. The Australian and US WP20 editions list different causes for this message, and older editions place board links differently, so note which book you hold.
Talk to us about manuals for your equipment. Send the make, model, serial number and software version (a photo of the label is fine) and we’ll help you find the right document.
When should you call us?
Call when the message stays after the site checks, comes and goes, follows a storm, or appeared after a board change. The measuring means two enclosures, one of them at the weigh frame, with readings taken both live and dead, so it’s a job for trained, authorised people working from the right document. If a board has failed, we’ll tell you straight whether to repair it or replace it. Call 1300 101 666 or email admin@accurateindustries.com.au with a photo of the screen and the boards. See booking a belt weigher service.
Frequently asked questions
Is bad scale comms the same thing as a scale data error?
Yes. Same fault, different generation: scale data error on a WP20 or WP25, bad scale card comms on a WP50.
My Tecweigh says bad scale comms. Are today’s tonnes any good?
No. With no load or speed arriving there’s nothing behind the rate or total. Treat the period as unmeasured, not low, and note when it started.
The scale was fine before the storm and now it won’t talk. Is a board dead?
Often, and the cable usually tests fine. Measuring each board separately shows which end took the surge.
We replaced a board and now it says scale data error. What did we miss?
Usually the termination links, or a card still set for the system it came from. Neither shows on a visual check.