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Noise can sometimes be introduced into a sensor input by a power supply or other high-powered equipment. Using a high-quality power supply is always a good idea.

Noise on the input is seen when the input value jumps around sporadically, especially for a normally stable sensor reading such as for temperature or pressure.

When there are alarms or digital outputs relying on this value, they can "flutter" as the value approaches their limit.

One approach to create a low pass filter by placing a capacitor between the sensor input and the sensor common terminals. This will allow the high-frequency "noise" to dissipate to ground while the steady sensor reading will remain on the input.

A capacitor in the range of 1 µF to 100 µF should be enough to eliminate most noise frequencies while not interfering with the sensor reading.

Start at the lower end of the range and increase the capacitance value until the noise has been attenuated to a satisfactory level.