Dimming and pulse are both proportional thermostat modes on Herpstats. The herpstat thermostats have a separate mode for on/off functionality.
The difference between dimming proportional mode and pulse proportional mode is as follows:
Dimming Proportional mode works like an automated lamp dimmer. It varies the amount of power being output to the heat source to regulate temperature.
Pulse Proportional Mode works similarly to an on/off style thermostat but without the swing that is associated with on/off style thermostats. Basically a pulse proportional thermostat fakes what the dimming proportional mode does. It does this by turning the power on and off extremely rapidly (like 60 or more times per second) This is called pulse width modulation. by varying how much time the thermostat outputs power and how much time the thermostat does not it can control the temperature of the heat source very accurately (although the dimming mode is slightly more accurate). This is very different to what an of/off style thermostat does, and shouldn't be thought of as the same thing (because it isn't)
An on/off style thermostat (or a herpstat in on/off mode) outputs 100% power until the thermostat achieves the desired temperature then shuts power completely off until the temperature drops below the swing temperature (usually - 2 degrees from the set point)
So what mode to choose?
dimming proportional is almost always the one to go with. It is the most accurate and is better for the heat source.
Pulse proportional mode should be used when there are grounding problems. Some metal racks hum/buzz when they have heat tape touching them that is being controlled in dimming mode. (Basically you should only use this mode if dimming mode is causing problems)
on/off mode should be used with heat sources that need a constant stream of power, or where accuracy isn't important. (like oil filled heaters)
Reply With Quote