Originally Posted by shortyjacobs
While a microprocessor does work in the digital realm, it's still relying on analog information. There is no such thing as a "digital thermocouple". Anything you use is relying on analog information.
Mostly, though, what I was pointing out that is that people seem to distrust an analog needle, but fully trust a digital readout, when both rely on the same information.
Shorty, you are WAY off base here, on more than one point. The difference between analog and digital really has nothing to do with a display vs a dial. There are certainly many electronic controls with dials and not displays.
While it's true that electronic controls are using an analog electrical input (variations in voltage, resistance or current), Analog temperature controls (like a Johnson A19, e.g) and Electronic Temperature Controls (like the Johnson A419 and Ranco 111-0000) sense the controlled medium (air, water) in a completely different way
. Analog controls have a copper bulb connected to a bellows in the control via a copper capillary tube. The bulb/tube/bellows are filled with a refrigerant (R-22, IIRC). The refrigerant pressure in the bulb expands and contracts in relation to the sensed temperature, making the bellows expand and contract. The bellows is linked to a micro switch, witch switches the load. There are a number of variables, chief of which is ambient temperature, which can affect an anolog controller. Suffice to say that an Analog controller is mechanical
, and therefor subject to all the susceptibilities of such devices. For example, prolonged exposure to a dusty environment can make them stick.
The typical ETC uses either a thermistor (JC A419, Ranco ETC, Love TS) or thermocouple (most PIDs, Love TCS), both of which are very stable electrical components, to measure changes in temperature. There are NO mechanical components, unless you want to call the relay mechanical.
I have used ALL kinds of temperature controls for a LONG time, and I can tell you that almost [I]any[I] properly fuctioning electronic control is significantly more accurate than almost
any analog control. When a dead band of 4-5 degrees is accepatable, then an analog control is fine. If you want more precise control, use electronic. That is the reason, after all, that such controls were developed.