Load cell specs

First time integrating load cells in a controller. How do I determine the characteristic value range (mV/V) if its not given in the load cell specs?

What do these parameters mean? Could I possibly derive it from this info?

Inputs: Maximum input voltage: +/-30 VDC
Maximum input voltage, ON: +5 VDC
Maximum input voltage, OFF: +2 VDC
Input current at +24 VDC: 5 mA

Outputs: Output voltage with no load, ON: +10 VDC
Output voltage with no load, OFF: -1O VDC
Minimum current (at limit): 6 mA

Power supply: Maximum current: 100 mA

dbm,

Welcome to the forum.

I am not sure about your specs listed, please give us the load cell and controller brand / model numbers.

Load cells are typically mv/v.

If they are going directly into a monitor, you need to see if the monitor can supply and receive the correct voltage signals.

If you are going into a plc, you will need a load cell amplifier that can supply and receive the correct voltage signals and trans mit it to the plc.

regards,
james

The Load Cell Specifications must be given:

Rated Capacity kG

Excitation Voltage VDC

Rated Output Voltage mV/V

etc.

assuming your load cells are standard wheatstone bridge type https://en.wikipedia.org/wiki/Load_cell

most load cells are 2mv/V or 3mv/V and that is usually stated on the specs plate.

Perhaps you are not looking at a standard load cell.

The specs seem to indicate a load cell with an integrated amplifier giving a +/- voltage output.

We really need more information on the load cell. Can you give us a part number. There should be a plate or sticker on the load cell that will give us all of the information. With the model number of the cell we can pull up some more detailed information. Here is a little more information on the specs.

mV/V - this is a proportion for the wheatstone bridge in the load cell. There will be "x mV" output per "V" input. It is also worth mentioning that if you are using multiple load cells, it pays to order "married" load cells. That means that this number on the cells is so close that you can simply "balance" the summing board (also called a trimming board). This is useful because rather than changing the resistance on the board to make the proportions close, you can simply set all pots on the board to the same value and you will get properly proportioned signals out of the board.

I really need to get some information in the manual to see about the rest of those values, but I can give you a bit of information. They may be these same values, but with a different name.

Generally you will have an "excitation" voltage. Think of this as the power supplied to the load cell. This makes the circuit work. You pass the excitation voltage through the cell.

Some cells have a sense voltage too. This is for load cells with multiple bridges together in parallel.

The last thing you will get back from a load cell is the "signal" voltage. This is the voltage or current input that is actually used to scale and measure the weight. It is worth noting that once installed into a scale a load cell will never have no weight on it. There is always the weight of the scale that gets factored in. How do they have you connecting the load cell to the PLC?

Thank you for all the responses. I really do appreciate all your insights.

The machine actually has a pair of load cells with an "Eilersen Electric" controller/monitor. I am to replace this controller with an s7-300 plc with the load cell connected to the siemens siwarex weighing module.

Upon ocular inspection I was unable to determine its part number and mV/V rating. In fact I didn't actually see any specs plate on the device.

The owner of the load cell just recently told me that the original load cells were replaced with that having a max capacity of 150 kg.

I am only able to work with these info given by the owner. It is quite unfortunate though that they are not that familiar with the specs. So I tried to manually determine the mV/V rating by measuring the output for certain weights and here is what I got:

EXC: 15 Vdc

10 kg = 12 mV
30 kg = 20 mV
50 kg = 28.4 mV

Is this enough for me to believe that the load cells are of 4mV/V rating?

Again thank you for all your replies.

What you really need is to get the scaling of the load cell (IE its output range for "zero/empty" load vs "calibration weight expressed as a point: (mV, weight) ). The actual range of the load cell only really matters when using a trimming board to utilize multiple load cells on a scale. If you are just using one load cell, you should be okay with getting you signal at scale/tray/belt or whatever the assembled scale consists of empty and then getting the reading with your calibration weight.

How do I determine a strain gauge from a digital load cell? Do they have different supply and signal connections? Are the connections: EXC+, EXC-, SENSE+, SENSE-, SIG+, and SIG- exclusive for strain gauge cells? or do all load cells have this type of wiring?
Sorry for being such a noob about this. Again no specs sheet and/or manual was provided with the load cell. Surely it had one before. Maybe it got lost or something?

I know the Eilersen load cells.
They old types were resistive full bridge load cells.
The latest types today have an integrated amplifier and send the signal digitally to a transmitter that in turn converts it to Profibus, Ethernet/Ip, 4-20 mA etc.
So there are no typical Excitation, Sense and Signal connection as with resistive full-bridge loadcells.

As always, specify the exact type no. Then you can get exact support rather than guesswork.