How It Works; Measuring Principle; Sensor Operation - Siemens SITRANS DA400 Operating Instructions Manual

Description

3.4 How It works

3.4 How It works
3.4.1

Measuring principle

Leaks in the delivery valves of oscillating displacement pumps are flows in which cavitation
occurs. This results in sound waves that are transmitted to the valve housing, where they are
recorded by the structure-borne sound sensor in the SITRANS DA400 on the outside.
The SITRANS DA400 utilizes the fact that with both an open valve and a closed intact valve,
no cavitation occurs and the measured sound level thus corresponds to the operating noise
of the pump. By contrast, with a closed defective valve cavitation does occur, which can be
identified by a period increase in the sound level (see figures). The measured value from the
SITRANS DA400 corresponds exactly to this increase in the sound level.
The measurement is carried out exclusively in the ultrasonic range. This filters out the
operating noise of the pump and the closing noise of the valves.
Figure 3-2
Figure 3-3
3.4.2

Sensor operation

The structure-borne sound sensor works on the piezoelectric principle. The structure-borne
sound is injected into the sensor via the sensor base (mounting surface) and inside it is
converted into an electrical voltage by a piezoceramic element. This is amplified in the
sensor and transmitted via the cable.
The sensor frequency range lies in the ultrasonic range (>20 kHz). The sensor is non-
directional, i.e. the angle at which the sound wave is incident on the sensor base is not
important.
3-4
Signal from structure-borne sound sensor with intact valve
Signal from structure-borne sound sensor with defective valve
SITRANS DA400 with protection against explosion
Operating Instructions, 02/2006, A5E00684661-01