Dirty power supplies

Off topic but the answer is here I'm sure. This little box controls the mix of plastic granules into an extruder. I have learnt from experience it is best not to take the 240v supply direct from the cabinet of the variable speed extruder. If power supply has any spikes or rubish then the display becomes incomprehensible, and the current recipe gets lost. The controller is a USA Colortronic VIC 31. Nice little unit - I often repair them, but this is such a common complaint that I could use a sure fix. I always say if I'm busy, just run an extention lead from the office to the factoy, and it will go OK. And it does. But is there such a device or a simple circuit that excludes all rubbish apart from 240v 50Hz?(say, the electrical equivalent of a 25 yard extention lead) Does this sound familiar to you people? Appreciate any views.
Jon.

Jonton,
Just use an isolation transformer for the color feeder power.

Walt

You may also want to look at installing line reactors on the incoming side of the inverter to prevent most of that rubbish being on the line.

As Waleye suggests, an isolation transformer is a good first step. Even better would be to specify the isolation transformer with an electrostatic shield. This further improves the noise isolation between the primary and the secondary windings and is not usually a big additional charge.

Thanks for replies. Ron, this client has many extruders and only two Vic31 boxes so I'll go for the easy fix. DickDV, does electrostatic shield mean earth-surrounded? or where is this shield? Do you mean between primary and secondry- these are quite common. Thanks again

To me, electrostatic shielding means a grounded shield between the primary and secondary windings. This tends to keep high frequency noise on the primary from coupling directly to the secondary thru, I believe, mutual capacitance.

An earth surrounded transformer, while a term I'm not familiar with here in the States, is likely a transformer encased in a grounded enclosure. This reduces the emission of noise from the transformer into the surrounding air and nearby conductors but doesn't do anything about coupling noise thru the transformer from primary to secondary.

Its the shield between the windings you want. It wouldn't hurt to have the grounded enclosure too but it might just be an expensive luxury.

If you have consistent power problems (voltage sags, ...) I sometimes use a constant voltage transformer. They're more expensive than regular xfmrs, but if it means the difference between a reliable system and not, then the costs are justified.

This is what I typically use-
http://www.sola-hevi-duty.com/products/powerconditioning/cvs.htm


I almost always keep PLC power supplies on seperate transformers from the rest of the 120VAC control power (to avoid spikes by motor starters, ...)

Judging from your topic description, the problem is noise from the power electronics of your extruder. A simple filter might be enough for your application.
You should also look into the possiblity, that you can minimize the generated noise from the extruder. Is the earth connection OK etc.

These are my general experiences with noise-beating equipment:

A filter with "spike" snubbers is best for noise that does not contain a lot of energy.
I had one of these explode on me. The reason was that the varistors that should cut off any overvoltage just couldnt take the amount of energy that originated from tyristor based regulation circuit for a melting furnace.

A constant voltage trf. (aka stabilizing transformer) can take more noise energy, and is excellent for places with "dirty" line power.
But it can only hold the voltage for less than a half voltage cycle (thats ½ x 1/50 sec = 0.01 sec). Anything longer will pass thru.

In the worst case one might have to consider a combination of a stabilizing trf. and a UPS.
The stabilizing trf. is the most costly item, so if there isn't a lot of noise energy in the line power, but there are power sags or "brown outs" then just a UPS is the most cost effective solution.