Heaters and Frequency

[DoubleL]

I know this may sound like a dumb question but I am having a brain drain today. A little background, one of my customers bought an used oven (but one my company built) from a company in England and this oven was set up to run on 415VAC 50hz. All they did here was to add a tranformer to change 480VAC to 415VAC. Now they are having problems with the oven reaching setpoint in the differnet zones. Are heaters and heater controls (Thyristers and SCRs) affected by changing frequency (50hz to 60hz)? Thanks, Double

[Ron_Smith]

I know for sure your heaters will not be affected by the difference... freq. is not an issue. Watts = V(volts) x I(amps) What kind of heater controls are you using?

[DoubleL]

Hi, Thanks for answering. The oven has Eurotherm 425A Thyristor units controlling the heaters. It consists of one as the master and the other the slave controlling two phases. The heaters are wired in star configuration. These are control via an analog card from the PLC. I looked at the Eurotherm manual but saw only one mention of any distinction between the frequencies and that had to do with firing times.

[panic mode]

well i didn't see one in longe time but it seams that firing time is the issue although it shouldn't if controller is doing good job. i thought this was thing of the past (simple RC delays in discrete timing circuits etc.) as nowdays microcontrollers are literally everywhere. modern controller should be able to measure line frequency (actually measure duration of halfperiod or time between zero-crossing) and scale 0-100% to fit and linearize that range for a sine.