Industrial Weigh Scales

[Onoff]

Picked up an industrial weigh scale. It was working. In fact a while back I replaced the grey cable to the control box as a favour.

It then died and they said I could have it. The 5-pin DIN socket on the load cell lead had had a tug and only green, white and screen were still connected inside the socket. Red, black, blue and yellow were all disconnected.

Load cell:

The load cell is this and has 6-wires plus screen:

I've looked inside the control box and wired it thus:

Pin 1 - Exct + Green
Pin 2 - Exct - White
Pin 3 - Screen
Pin 4 - Sign + Red
Pin 5 - Sign - Black

I've not connected the blue and yellow from the load cell.

Plugging the load cell into the display and I can zero the unit OK.

Putting any weight on the scale though and it throws a hissy fit. A warbling siren sounds and the screen flashes "under'.

Anyone any experience of these?

Cheers.

 

[Misterg]

Pin 1 - Exct + Red
Pin 2 - Exct - Black
Pin 3 - Screen
Pin 4 - Sign + Red
Pin 5 - Sign - Black

I've not connected the blue and yellow from the load cell.

What about the green and white? (Signal + & Signal - according to the photo of the label)

 

[Onoff]

What about the green and white? (Signal + & Signal - according to the photo of the label)

Whoops! Just corrected my post. The green, white, red, black & screen are connected.

I then just tried it like this, connecting the blue and yellow...and that didn't work either

Thanks.

 

[Hopefuldave]

Wheatstone Bridge cell - is it on a 4-wire or 6-wire cable connection? the Sense connections are paralleled with the IN+ and IN- to compensate for voltage drop on the IN cables between readout head and sensor (SENSE inputs at the readout are high-resistance, so the cable resistance back from the cell to the readout's not affecting the measured voltage, which thanks to the cable voltage drop is different from what the readout puts out on IN), if the cable's short they can be connected inside the readout (or its plug, or at the cell's plug) instead of at the load cell, without that the readout doesn't have an accurate reference and that could give the "under" warning - if the SENSE connections aren't made, it could be trying to deliver volts it can't see to the load cell and ramping the voltage up (to whatever it can deliver) to try and see the feedback on SENSE, not seeing the right voltage and flagging the undervoltage coming back on SENSE.

 

[Onoff]

Wheatstone Bridge cell - is it on a 4-wire or 6-wire cable connection?

It's a 6-wire cell. Only 4 wires to the digital readout. I did try it like this but to no avail:

 

[Misterg]

What connections are there in the box?

 

[Onoff]

What connections are there in the box?

Exct +
Exct -
Sign +
Sign -

 

[Misterg]

Exct +
Exct -
Sign +
Sign -

So, following the colours on the photo of the label:

RED from the load cell should go to EXCT+
BLACK from the load cell should go to EXCT -
GREEN from the load cell should go to SIGN+
WHITE from the load cell should go to SIGN-

(I can't figure out whether you've already tried this combination or not...)

 

[Onoff]

So, following the colours on the photo of the label:

RED from the load cell should go to EXCT+
BLACK from the load cell should go to EXCT -
GREEN from the load cell should go to SIGN+
WHITE from the load cell should go to SIGN-

(I can't figure out whether you've already tried this combination or not...)

I'll double check and try that combo. Can I leave the black and yellow disconnected?

 

[Onoff]

Inside:

I've wired it like this:

Still the unit is going haywire!

 

[Misterg]

Can I leave the black and yellow disconnected?

BLUE and yellow? Yes.

Still the unit is going haywire!

Try swapping the SIG+ and SIG- around.

If that doesn't work, disconnect it and measure the resistance between:

EXC+ and SIG+
EXC+ and SIG-
EXC- and SIG+
EXC- and SIG-

 

[Onoff]

BLUE and yellow? Yes.



Try swapping the SIG+ and SIG- around.

If that doesn't work, disconnect it and measure the resistance between:

EXC+ and SIG+
EXC+ and SIG-
EXC- and SIG+
EXC- and SIG-

Not yet swapped over SIG + & SIG - but:

Between:

EXC+ and SIG+ = 277ohms
EXC+ and SIG- = 277ohms
EXC- and SIG+ = 277ohms
EXC- and SIG- = 277ohms

All pretty much there or thereabouts, within an ohm or two.

 

[Hopefuldave]

Those resistances are spot on, the Wheatstone bridge will have equal resistances at rest - that's how they work, varying one of the resistances give a voltage across the mid-points (Sig+ and Sig-).

The board has Sens + and - terminals, if all else fails try linking Exc+ to Sens+, Exc- to Sens- in the box on that 6-way connector.

Has it worked before as wired, is it *exactly* as wired when it was working?

 

[Misterg]

All pretty much there or thereabouts, within an ohm or two.

That's good - I think the load cell is intact.

(Make sure you connect the screen up, too.)

I presume that the terminals marked Sen+ & Sen- in the box have always been empty?

[Edit: Sorry @Hopefuldave - post crossed]

 

[Onoff]

Has it worked before as wired, is it *exactly* as wired when it was working

It was working but as aforementioned the 5 pin socket on the end of the load cell cable had been pulled. Could be someone else had had a go before I got it.

 

[Onoff]

I presume that the terminals marked Sen+ & Sen- in the box have always been empty?

Yes, 100%. I replaced the grey cable on the box a few months ago.

 

[Hopefuldave]

It was working but as aforementioned the 5 pin socket on the end of the load cell cable had been pulled. Could be someone else had had a go before I got it.

Well, *something* or *someone* made it stop working... Unless there's a pair of jumpers to select 4 or 6 wire in the box or some other way to tell it which, the connector definitely has empty spaces... I'd take a chance if there aren't a couple of obvious jumper pins (probably right behind the connector on the PCB - a good pic straight on and well lit would be handy) and link as described above - someone could have lost the links faffing about with it?

 

[Master-of-none]

Can I suggest adding some load to the scale and then re-measuring the resistances, to see what changes.

 

[Onoff]

(probably right behind the connector on the PCB - a good pic straight on and well lit would be handy)

https://flic.kr/p/2pbtqgY

https://flic.kr/p/2pbtTLi

 

[Hopefuldave]

Cheers - looks like J2 and J3 by the fixing screw are in a likely spot, and as they're jumpered it's probably already linked for 4-wire, so can discount that...