For an application a temperature sensor is required. an accuracy of around +-3 degrees is acceptable.
For cost reasons I have chosen for this RTD. The sensor is sampled by a 12 bit ADC of an Microcontroller. The RTD is placed in an wheatstone bridge with a regulated 3.3v supply (looking at the supply with an scope I did not find much noise/ ripple). The Wheatstone Bridge is connected to an MCP6N11 Instrument amplifier.
The RTD is mounted on a separate board with about 50cm of wire, which runs through a noisy environment. Therefore the filter stage is placed between the bridge and amplifier.
The desired temperature range is between 50 and 200 Celsius. The gain of the amplifier is set to 15, and is supplied by a single 3.3v supply.
Unfortunately, the measurements are constantly off by 30 to 50 percent. As well as there is still some noise sneaking through the filter. The amplifier is connected directly to the 12 bit ADC.
What can i do to improve this circuit?