I was working with a customer to replace a Siemens clamp-on ultrasonic flowmeter after its electronics had been replaced.  We followed all the connection and startup instructions, but the flow rate was stuck at 0.00 – no dithering, no hunting, not a single flicker in the low-order digits.

Very strange.

Ultrasonic clamp-on flowmeters can be very sensitive to low flows. But even at no flow with the pump turned off or the line isolated, the digits to the right of the decimal point would dither around zero, showing some very small positive values, some very small negative values.  It’s the nature of the beast.

So why were we getting an absolute zero reading? What was going on?

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