Assets

Product features

Continuous and independent status monitoring:

• Of the flow control valves, for leaks
• Of the membranes, for material fatigue
• Of the temperature loading of the hydraulic oil
• Of flowing bulk solids in pipes, conveying equipment or channels

Communication of the status to superordinate control systems:

• Via digital outputs
• Digitally, via PROFIBUS DP or PROFIBUS PA

Simple to operate and parameterize:

• Locally, via digital display and keys
• PROFIBUS DP and PROFIBUS PA

Mode of operation

Principle of measurement

Leaks in the flow control 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.

In the version for material flow monitoring, SITRANS DA400 continuously detects high-frequency acoustic oscillations by means of structure-born noise sensors.

These oscillations are created by:

• Friction and impact of bulk solids in:
  • pipes, raceways or channels
  • chutes
  • conveyors
• Friction and impact of mechanical parts
• Bursting of bubbles
• Cavitation
• Turbulence in gas and liquid flows

The following shows an example of signal levels at an oscillating displacement pump

Signal from structure-borne sound sensor with intact valve

Signal from structure-borne sound sensor with defective valve

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 piezo-ceramic 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 impacts on the sensor base is not important.

Mode of operation of the safety barrier

The safety barrier comprises intrinsically-safe circuits. These circuits serve to operate intrinsically-safe components such as sensors and to isolate safety from the non-hazardous area with the SITRANS DA400 diagnostic unit.