Template:Thermocouple 50 60Hz Filter

50Hz/60Hz Filtering

One of the most common sources of electrical noise in a system is 50Hz or 60Hz hum from local power grid. For firmware versions {{{1}}} and later for this Phidget, we have added a filter to compensate for 50Hz or 60Hz hum in your system. This means you can worry less about this problem in your application.

Without filtering, sensors in electrically noisy environments could see a repeating drift of tens of degrees, as noise from power lines finds its way into the system. The timing of this drift could vary, depending on how the samples from the sensor lined up with the noise from the power lines.

To combat this issue, all thermocouple temperature and voltage measurements on this device are now passed through a 100ms moving average filter, with samples taken at specific intervals designed to cancel out frequencies of 50Hz and 60Hz (the most common power grid frequencies). The filtering on this Phidget will reduce the effect of power line noise by 95% or more, becoming more effective as the power line frequency approaches 50Hz or 60Hz exactly.

All samples from the sensor will be subject to filtering. When used with data intervals longer than 100ms, the sensor will measure the thermocouple(s) for 100ms to perform a measurement. When using data intervals less than 100ms, your application will see the effects of the latest measurements as they pass through the filter.