In an experiment, the transducer showed -1.9 Bar pressure. How is it possible? I was doing an experiment on water hammer in pipes. During the experiments, in several cases, the transducer reported negative pressure, as low as -1.9 bar gauge! But I have read that it is not possible for the pressure to practically go beyond absolute zero. I thought it might be due to some calibration issues of the transducer, and recalibrated and double checked the experimental values. I did the same experiment again. But the pressure shot down to 1.9bar or 190 Kpa below gauge, when cavitation occurred inside the pipe.
The pressure transducer i am using is a 0-30 bar transducer (forgot the company name), and i am measuring the values at 50,000 samples per second. the operating pressure inside the pipe in steady flow conditions is 1.7bar gauge and it is being shown correctly.
Can anyone give a possible explanation for the same?

The graph denotes the actual pressure vs time graph obtained during the analysis. the sampling frequency is 100000Hz and the Amplitude shows pressure value in bar, in gauge scale. The time scale is shown in 10microseconds value
 A: The sensor measures push or pull force on a plate, and, using the area of the plate, translates that into pressure. There are multiple ways to get a "pull" force on the plate without negative pressure. Inertia from moved sensor, internal pressure in the sensor,...
Sensors only perform as expected if they are used within their limitations. Imagine a diaphragm displaced by air under pressure. the amount of displacement somehow is translated into a pressure reading. Now that pressure is removed fast. The diaphragm will bounce back, and without any air to stop it, it will move further than its ususal "0 pressure"-position, for a short time, then resettle on the "0 pressure"-position. This will then be read as "negative" pressure.
The ability to answer to changing pressures, or pressures baove/below certain thresholds is one factor that drives the specialisation of sensors. (Medium, accuracy, drift, etc. are other factors.) Not every sensor will be able to measure every sort of pressure  & pressure-change reliably.
A: Water hammer in pipes will exhibit transient pressure spikes that go both positive and negative. When they go negative, cavitation can occur. Therefore, if you observed cavitation in the experiment, then it is evidence that the pressure in the system did indeed go below atmospheric for a brief time. 
