Hardy Process Solutions

Question

How do I get an accurate reading on my conveyor scale?

The approach I´m using right now is a photocell mounted on the small conveyor. When a box is detected by the photocell I capture the weight data from the PLC, but the data captured varies too much.

If I stop the conveyor and I put a box on top of it I get the right weight.

What should my WAVERSAVER and Averages settings be?

Answer

This is talking about a check weighing application and not a belt scale application.

The big question here is what is the amount of time the box is in the scale section? If you are using the photocell to signal when to capture the weight, you would want this to be placed towards the end of the conveyor, so the weight is captured at the last possible moment. This way, you have the maximum time on the scale to allow the weight to settle. If the box is not on the scale long enough for the scale to settle, then you will get varying weights.

The WAVERSAVER setting will remove the effects of vibration on the scale. The higher the setting, the longer the delay from this operation. The way to set the WAVERSAVER is to reduce your averages to 10, and set the WAVERSAVER setting to the lowest setting. Monitor your weight readings with all equipment running, but no product on the scale. This will show you the maximum fluctuation of the system due to noise and vibration. Now increase your WAVERSAVER setting up one setting level. Monitor the fluctuation to see if it lessened. Make another increase in the WAVERSAVER setting and see if the fluctuation got better again. Continue this until the change does not make any significant difference. Once you reach this point, back off one setting to the previous setting.

The averages will dampen any fluctuation in the weight readings. If the update rate is 50 times/second in your controller, for every 50 averages there would be a 1 second update delay. You can increase your number of averages until you have a stable reading. This will be the fastest reaction time providing a usable weight reading.

The update rate for specific Hardy controllers are:
HI 2110WI = 50msec
HI 2151/30WC = 50msec
HI 2160RC = 50msec
HI 3010 = 18msec
HI 3030 = 18msec
HI 3300 = 18msec
HI 3600 = 18msec
HI 4050 = 9msec
HI 4050CW = 9msec or 4msec depending on setting.
HI 4060 = 9msec
HI 6300 = 20msec
HI 6500 = 9 msec
HI 6600 = 9 msec
HI 1746WS = 50msec
HI 1756WS = 20msec
HI 1769WS = 10msec
HI 1771WS = 50msec
*HI 200DNWM = 10msec or 100msec, depending on the WAVERSAVER™ setting.

If the box is not on the scale long enough to obtain a stable weight, you need to slow down the system to allow enough settle time to read a stable weight.

The factors that cause the delays in achieving the final weigh readings are as follows.

WAVERSAVER = 7.5hz (60ms) to 0.25hz (2 second)
Averages as described above
Load cell reaction time. Range 100ms to 500ms
Entering and exiting the scale. You must be fully on the scale to collect the weight reading.
Spacing between items being weighed.

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