Ab Plc For Conv Scale

micah123

Guest
M
You guys were a lot of help last time, thought I'd try another problem on you. My company is putting in a new mixer (rubber) and are putting in a measuring and weighing system to feed it. My task is to connect a plc to the weighing conveyor load cells and then determine proper amounts for each item to put into the batch. I have a SLC-503 and a MV/thermocouple card (on my desk). I connected a load cell simulator to the first input and used 3 resistors to give me 30mv at 15 volt excitation on the second input. Then calculated the weight in the logic. This seems to work pretty good and the load cell simulator switched to different positions is within 2/10ths of a pound all the way up to full scale (1000lb). I even varied the excitation from 2 volts to 15 volts and the calculated weights were still within 2/10ths of a pound. What I want to know from you guys is has this been done by any of you, if so how did it work in the field, also I haven't purchased this stuff yet. The SLC503 may be the same one that runs the mixer or it may be stand alone, If stand alone I may use a micrologix 1200 and a TC/MV card with it. I've done this using a regular weigh scale years ago but we lost some accuracy by converting the weigh scale to analog and into the plc. What about a weigh scale card for the SLC-503? Anybody make one?
Load cells 2mv/volt @ 1000lb.
 
mV?

What about a weigh scale card for the SLC-503? Anybody make one?

Yea, for this you'd want to look at Hardy. They make a card.
Of course, Mettler-Toledo makes scales with Remote I/O
interface, but then you'd need a 1747-SN module in the 5/03
to read it.

You've got bigger things to worry about with the 5/03, such as
the interface to your data entry device for the batching information...

Why not just enter the weight information into a 'batchable'
weight indicator, like a Rice Lake 810, and let the Rice Lake
tell the PLC when to add what.

Then, the Rice Lake will be the operator interface for the
batching, and you're done!

Either way, a Mv card is hardly the same as a scale unit.
Others will likely chime in on this issue.
 
I made some mixers for bakeries. We use to weight the water and flour
before they go down to the mixer.
We used analog input 4-20mA, BCD and RS232 with AB 5/05 and 5/03 CPU.
for $300 you can get Red-Lion PAX with analog output.
You can get weight disply and scealing option.and analog/rs232 com output.
I had 5 analog inputs in my mixer so it save me a card (I used 8 analog input card).
It mach easy and reliable then to deal with mV.
 
more cost effective solution

the rice lake 920I indicator is fully configurable to various outputs and inputs with its optional cards. We use it for a similar operation.the indicator itself is 1200 dollars canadian. and is a nema6p rating on water integrity. you can program it with any configuration desirable and it has all the capabilities a standard PLC would provide.
 
As for using a scale, I have to be able to select different batches on an operators panel. The different recipes will determine the setpoints for weight and what material to be weighed at what time. The plc will do the recipes but I first have to have the weight available inside the plc. If I use a weigh scale, I will have to input to an analog card or remote I/O. What I was hoping for is a SLC card that I could just hook straight to the load cell to and read the weight on a data table. So you think the MV signal might be a problem to work with in the plant environment?
 
By the way, I just looked at Hardy online and this looks like what I need, I'll be getting some info from them and go from there. Thanks..
 
the problem I foresee is the zero tracking and maintaining stable calibration setpoints. Most scale indicators have several different parameters that are used for signal correction such as filtering ztrack, zeroingx linearity adjust etc the list varies from indicator to indicator. The other problem your going to face is that if the scale requires certification ie in a final weight for customer sales then certain parameters are required by weights and measures. Of course these are the Canadian requirements but I would imagine that the US would have a similar regulation. By the way the voltage on the signals is measured in mv/voltohms
 
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