Fill by weight

[CharlesM]

We are looking at an application where we will be filling a container by weight. The current system uses a large hopper on top that feeds two vibratory feeders. Then a small hopper with a scale to do the weight. This should be simple to do in a plc however they are currently using a scale system. I am thinking their scale system is running some kind of PID to slow down the feed as it gets near the setpoint. How important is the scale controller? Can I do this in the plc? I have never done this type of application but it looks like I should be able to do it in a plc.

Here is the spec's as I know them.

Part weight 3400 grams
Fill time 30 seconds
+/- 2 grams

[panic mode]

you are on the right track. i've done programming on practically same thing (with 3 or 4 filling heads on same machine and control system). target weight was 7-20kg, +/-30g, fill time was 5-6 sec for each filling head. measurement was done with loadcells, everything was controlled by small PLC. Due short cycle time, and vibrations, challenge was to get accurate weight reading (I wish I had 30 seconds).

[mordred]

I've yet to see a scale indicator that has PID functions possibly its sending an analog signal to a PLC this can be done exclusively in a PLC unless there is an issue with American weights and measures. If so then one route you can do is have a scale indicator that has an optional analog output card 920I from Rice lake has this feature. Or you can send an ascii text on a standard indicator set for constant transmit to send the data to the PLC. perhaps you can post the scale indicator make and model if it has PID I would be interested in knowing what it is

[CharlesM]

Here is the controller I was looking at

http://www.hardyinstruments.com/proc...ser+controller

The scale part itself is not a problem. I just worry about the fill logic. Can it be turn on output till >= set point or does it need to be an analog output that slows the feeder as it gets close to setpoint.

[Controls_Engineer79]

well you could do it both ways

but with the set points - maybe have it filling at full speed till it reaches 90% then have it slow down at that point till it reaches 98% then slow down even more

have more then one set point will give you better +/- control

[Longhorn]

I am not familiar with your application / equipment but have a good deal of experience with liquid fillers. A common approach is to "fine fill" for the first few percent then "coarse fill" until the container is a few grams (say 200g) from the target weight before switching back to fine fill to achieve the target weight.
Hope this helps!

[bernie_carlton]

Longhorn - just curious, why the initial 'fine fill'?

[Banker]

It can be done in a PLC. But you have be aware of the amount you are filling after you stop. Is it a valve or a belt. If you have a "noisy" weighing signal because of vibration there can be an problem there. To long filter time on the weight signal can cause a signal delay.

Banker

[CharlesM]

Good inforamtion guys. I was waiting to see if anyone said "no don't try this in the plc" or look at one of these controllers.

I think we will be using a vibratory feeder or maybe a conveyor. One thing I have working for me is time. I think I can go through a few steps in the filling process because I have time to do it.

[Gummit]

Good load cell meters have "in-flight" compensation.

In

-flight compensation allows the filling system to switch off the filler valve
before the correct weight has been reached. This may be required if some of
the product could be delivered for a time after the filler control valve has
been switched off. The In-flight compensation can be applied to both the

main feed and trickle feed controls outputs.

http://www.datatrackpi.com/panel-met...-load-cell.htm

[widelto]

Originally Posted by bernie_carlton

Longhorn - just curious, why the initial 'fine fill'?

It must be the opposite first coarse fill and fine fill at the end.

[widelto]

Originally Posted by CharlesM

Here is the controller I was looking at

http://www.hardyinstruments.com/proc...ser+controller

The scale part itself is not a problem. I just worry about the fill logic. Can it be turn on output till >= set point or does it need to be an analog output that slows the feeder as it gets close to setpoint.

Charles:
I´m in charge of designing a system to fill containers with edible oil ( 14 & 20 liters) maximum time is aprox 20 secs per container, I want to use the same controller HI 3010 or use a compactlogix (1769-WS) with hardy C2 load cell ( no calibration needed ), just waiting for quotations and then compare controllers (3 or 4) Vs. compactlogix solution.

[JeffKiper]

I just climber out of our mix Towers. We have 17 scales from just about every make and model.
CharlesM you did not say what PLC you where using. I have only set up 1 weight system in a PLC (AB SLC 5/05) all the rest I just support. I like using the in chassis card made for scales. We uses Hardy on the one I setup. If you choose to use an analog version scale it to real numbers.

We have a Hardy HI 3010 in 1 of our operations it works nice.

[CharlesM]

I want to use the same controller HI 3010 or use a compactlogix (1769-WS) with hardy C2 load cell ( no calibration needed ), just waiting for quotations and then compare controllers (3 or 4) Vs. compactlogix solution.

It would be good to see which one you use.

CharlesM you did not say what PLC you where using.

I will be using Siemens.

[SMOKE]

I once ask Pete if Delta made a scale interface. He said that they had made some customs. I would talk to him.I have done lots of filling in the past, using Sartorious, and metler scales, as well as load cells.I think you will find you will have to pulse your feeder when your near your target weight. Update time is issue, and if you use a PID it is hard to compensate for update and material in flight.I typically use a volume gross fill and finish with flat vibe.