Do I have to replace my Tecweigh WP20 or WP25, and what changes on a WP50?

We’re an independent service company, not a Tecweigh dealer or agent, and we’ve no Tecweigh product to sell. If you’ve got a message on the screen rather than a decision to make, see WP20 and WP25 fault codes and calibration. For what a service covers, see Tecweigh belt weigher servicing.

Which processor do you have?

Look at the boards inside the enclosure: the WP20 is built on an MP400 board, the WP25 on an MP600, and the WP50 on an MP800 main board with a separate DI400 display board. The power-up pass message is a quicker tell: it reads as a self test on the WP20 and WP25 and a self check on the WP50, so a photo of the screen at power up usually tells us which one you have.

When would we recommend a change-out?

Age on its own isn’t a reason. These are the differences that actually drive a change:

• A fault contact. A WP50 relay can be set to operate on a scale communications, load or low power error, so the control room sees a scale fault. The WP20’s relay offers a total pulse, rate and speed alarms and a span output. The WP25 adds more alarms, including a zero tracking limit, but neither has a fault output. On those, only someone walking past the display knows the scale has a problem.
• A calibration safeguard. The WP25 and WP50 show the percentage change after a zero or span and ask you to accept or reject it. The WP20 keeps whatever it measures.
• Memory. After a memory fault the WP20 restores its settings from its backup copy or from factory defaults, which its manual puts down to battery failure or an electrical spike. A power event can take the calibration with it.

If an enclosure keeps taking damage, fix that at the source first (protecting belt weigher electronics). If a purchase is on the table, see five questions before you buy a belt weigher integrator. 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. Talk to us about replacement options. We’ll tell you straight whether to repair it or replace it.

Why can’t PLC code for a WP20 be copied to a WP25 or WP50?

When the plant asks for status over the serial link, the processor answers with a single character, and the meanings differ by generation:

• WP20: eight meanings. Positive rate (normal), negative rate, zero cycle, zero tracking, span cycle, high or low alarm, weight processor error and, last, low battery.
• WP25 and WP50: seven meanings, and the last one is a load error.

Copy WP20 code onto a newer unit and a genuine weighing fault arrives in the control room as a low battery notice, which plant code usually logs quietly. The rate and total keep looking plausible, so the first sign is often a reconciliation that won’t close months later. And code watching for the WP20’s weight processor error will never see it again.

Re-map the status character from the document for the unit actually fitted, then prove it by forcing each condition and watching what the PLC receives. Fieldbus tag maps don’t carry across either: each generation’s card has its own document, and the WP50’s optional daughter board covers Modbus TCP, EtherNet/IP and ProfiNet. See getting WP50 faults into the PLC and getting belt weigher data into your PLC or SCADA.

Which messages were renamed rather than removed?

Search the WP50 manual for the old wording and you can think the message is gone. Usually it isn’t:

• Scale data error on the WP20 and WP25 is bad scale card comms on the WP50: the main board has lost comms with the card at the scale.
• Framing error is bad auxiliary comms: a framing error, corrupt data or no data on the auxiliary serial port.

Same conditions, same checks. The WP20’s power-up fieldbus scan message is genuinely gone, and the WP50 adds messages the older units can’t have, such as a fault on the link to its separate display board. See what the messages on a WP50 mean.

What happens to your totals?

The structure changes at each generation:

• WP20: a single total, which has to be reset once it reaches its upper limit.
• WP25: a short and a long total. Resetting the long total resets both and adds the long total to an odometer.
• WP50: three totals plus a lifetime odometer. Resetting Total 2 also clears Total 1 and updates the lifetime figure. Total 3 can’t be reset by a user; it rolls over at its ceiling.

Wire a WP50 reset input to Total 2 by mistake and a single pulse clears two totals and moves the lifetime figure. Map totals by meaning, not position: the WP50 manual says its Total 1 equals the WP20’s total and the WP25’s short total.

The WP25’s maintenance menu also lets the stored zero counts, span counts and odometer be changed by hand, so a figure on a screen isn’t evidence on its own. A written record from the day is.

Does an open interlock still stop everything on a WP50?

No. On the WP20 and WP25 an open interlock disables the rate, the totalising and every output. On the WP50 it only pauses the totaliser. Plant logic that inferred the interlock from a dropped rate will stop working, and a live rate beside a still total looks like a totalising fault. The WP50 does show the interlock in its alert queue.

Any of the WP50’s four digital inputs can be the interlock, and the same inputs can reset totals or start a zero or span, so read the input assignments off the unit rather than assuming them.

Can a WP50 share a line with older processors?

Yes. In polled query mode up to sixteen units can share a multi-drop line, and the legacy data format lets the WP50 be daisy chained with WP20 and WP25 units using the same data format. The manual doesn’t say the legacy format restores the old status character meanings, and we haven’t tested it, so treat the data fields as portable and prove the status character on the unit before code relies on it.

Before pointing a new controller at an old WP20, note that its serial link accepts remote zero and span commands.

What changes out at the weigh frame?

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.

On a strain gauge frame, the card at the frame isn’t automatically scrap: the WP50’s low power alert names three generations of scale card, and its alignment instructions cover earlier cards too. Check the card on your scale. We don’t quote supply voltages here, because they differ by card, processor and power supply version, and the Australian WP20 manual gives two different figures in the same book.

A displacement carriage is a real retrofit. The speed sensor and data cabling move to the new card, an interface board replaces the older card and takes the displacement sensors, and the spare cord grip is plugged. The current card doesn’t read in the negative direction the way the earlier one did, so each sensor is reset to a slight positive bias, one at a time, and the scale is recalibrated from scratch (belt weigher calibration methods). It’s a job for someone who has done it before.

The cable limit between the processor and the frame card is roughly 1,200 m on all three generations, so a marginal run stays marginal.

What’s different for whoever calibrates it?

• Starting a cycle. On the WP20 a zero or span is a five-second press and hold, and the total clears by holding the reset button. On the WP25 and WP50 it’s a momentary press and a yes or no prompt. A tech used to one can report a dead keypad on the other.
• Accept or reject. On the WP25 and WP50, a large change on a scale nobody touched is a reason to reject and investigate.
• Security locks. On the WP50, locking the zero, span and total resets only locks the keypad. The same commands still work over a digital input, the serial port or the fieldbus. A remote zero or span is refused if the change would be more than about 5%, and then has to be done at the keypad. See locked out of your integrator.

What should be recorded before anyone swaps a processor?

The old unit usually leaves site the same day, and anything not written down goes with it:

• every stored parameter, read off the unit
• the as-found zero and span figures
• every total at the moment of the swap, including the lifetime figure
• the running rate with the calibration weight applied

That last one is the only way to tell later whether the new setup drifted or was never right. If you export a WP25’s calibration log, do it on a stopped belt: it only exports during a start-up, and a setting can erase the records afterwards. We record as-found and as-left figures on every visit and keep each scale’s configuration in AIMM, our asset management system, so a change-out starts from a written baseline.

Need a manual for your equipment?

A change-out needs the manual for the processor coming out, the one going in and, on a displacement carriage, the card at the frame. Editions differ on link positions, supply voltages and message wording, so match each book to the unit and its version.

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?

Before a change-out is ordered, not after. We’ll check the frame, the card and the cable run, and help map the PLC status and totals across. Call too if a WP20 or WP25 won’t calibrate or hold its zero. Phone 1300 101 666 or email admin@accurateindustries.com.au.

Frequently asked questions