Signal Wiring & Power Wiring
Signal wiring deals with input signals (generated by the temperature sensor) and output signals (generated by the temperature controller).
Power wiring deals with supply power to the temperature and power controllers and the current that is ultimately delivered to the heating element.
Signal wiring is less straight forward than power wiring. Not only does it have to conform to circuit design but also installed in such a way as to minimize the negative effects of electrical noise present in any thermal system.
What Is Electrical Noise?
Electrical noise from all sources and its effect on controllers are very difficult to define, let alone give exact rules on how to prevent. Noise sensitivity is a function of more recent electronic controller designs. However, the majority of noise problems stem from crude wiring practices and techniques, which allow “coupling” or the transfer of electrical noise into the control circuit.
When Is Electrical Noise a Problem?
Some other commonplace symptoms are fluctuating digital indicators, blanked digital indicators, control instability about set point, and outputs turning ON or OFF unexpectedly.
Another red flag of electrical noise raises when high or low limits trip with no limit fault condition.
Why Is Electrical Noise Sensitivity a Problem?
The development of all electronic solid state controllers has improved the accuracy of control and expanded immensely their capabilities, but they are more complex and operate at very low power levels. Electrical noise is more likely to affect them because of their lower operating power levels.
Where Does Electrical Noise Come From?
- Switches and relay contacts operating inductive loads such as motors, coils, solenoids, and relays.
- Thyristors or other semiconductor devices which are not burst fired (randomly-fired or phase angle).
- All welding machinery.
- Heavy current carrying conductors.
- Fluorescent and neon lights.
- Thermal voltages between dissimilar metals that influence the low voltage thermocouples input signal.
- Chemical voltage produced by electrolyte action between poorly connected leads and interconnect cables.
- Thermal noise from increased ambient temperatures around the circuit electronics.
- Noise could be introduced if the control circuit includes the option of a mechanical relay output and is used to switch high load currents over two or three amps. This presents a significant source for noise, including inductive noise from the coil and contact arcing, depending on how much power is brought inside the controller.