What is dither and how does it affect the flow measurement?

Signal dither is a potential source of measurement error. Dither occurs when a meter generates an output when there is no net reportable flow. This is usually observed at low flow or zero flow conditions. If the meter misinterprets vibration or pulsing liquid motion it will over report the actual flow rate. To prevent this error, the flow meter must detect flow direction and buffer or ignore the change in flow. Common techniques are to use a quadrature output which will produce an alternating A pulse then B pulse. If the meter starts to dither, this output will reverse the pulse phase or possibly create a sting of “A” pulses. Special electronic displays that accept two pulse inputs can ignore the erroneous signals. For simplicity, Max transmitters use a sophisticated sensing system that tracks the meter’s position and detects the dither before producing its frequency output.