Mettler Toledo scale & RSLogix

I’m having a little problem with the finishing touches on integrating a Mettler Toledo scale. I have a WMS204, setup with an Ethernet/IP module to plug straight into my CompactLogix network. I have communication all the way through to my CompactLogix, no issue there. The problem that I am having though, is that the weight value (.WV in the AOI) is coming across being rounded to the nearest whole number. The weight of the apart I’m testing is 146.12. When measured through the logic in the PLC by use of the AOI, I get a reading of 146.0. When I connect to the ConBlock & use HyperTerm to query the weight (which is their method of backdoor access to the weigh module), I get the measurement of 146.12.

The funny thing is, that if I place something on the scale with only one digit to the left of the decimal, then the AOI will give me a readout of 1.312546 (I’m pretty sure its 6 places to the right, it might only be 5 though). If I place something with 2 digits to the left, that it rounds those numbers to 2 decimal places, i.e. 52.27.

I’m using units of grams, no issue there on the values coming across, just this weird rounding thing. I’m not sure if it being lost in the value coming across being a DINT, and the .WV value of the AOI being a Floating Real number? I can’t seem to make it work out though.

I'm not sure if anyone has integrated a MT scale on RSLogix before or not, but I thought I would put out feelers for some help. Thanks in advance!

I've not used that model, but have used the IND131 and IND331 with Logix PLC's quite a lot. If it integrates the same way as those, you have an option to send the data back in DINT format or floating point format. Obviously, you want floating point. You will need to set it in both the parameters of the MT unit and also in the ethernet parameters in Logix (assuming you're using an AOP or similar).

Be aware that the methodology that the MT uses when set to Floating Point data is quite different to the methodology it uses when set to INT data, so you may have to dig out the manuals and do some re-work.

Of course, all of this is assuming that your unit works the same way as the ones I'm familiar with, which could be completely untrue!

Hi, can you guide how to use the Zero and Tare commands remotely from the PLC for IND331 using RSLogix5000 and Ethernet/IP. I'm using Integer values for scale not floating point.

Have a look through the PLC interface manual. There is a table showing a list of all the commands you can send to the device, which includes the zero and tare commands. I have only ever used floating point, and I'm not sure if sending the commands is done the same way with integer and floating point or not - but all of that will be in the manual as well.