ESGI#47

Danfoss Industrial Controls:

Mathematical analysis of the dynamic flow characteristic in a damping nozzle for a pressure transmitter.

Purpose:
To set up

an approximate but in practice usable method to calculate the bandwidth in stationary operation and
a description of stages in possible start-up situations.

Background:
The "Puls-Snubber" (see figure 1) consists of a hole about ø0.3x0.5. At the input side is the media pressure and the output side looks into the "dead volume" about 1500

. The media can be gas or liquid, for instance air or hydraulic oil (32 cSt by 20C). The pressure in the dead volume is mea- sured by an incompressible pressure sensor with infinite band-width. The housing can be considered incompressible compared to the bulk-modulus of the media. The media in the dead volume can by start-up be anything between air, a mixture or liquid. The air in stationary operation will partly be dissolved in and partly removed by the initial liquid transport through the nozzle.

Function:
The function of the nozzle is to prevent cavitations in the dead volume which can damage the thin sealing diaphragm. The band-width by the pressure measurement should be reduced as little as possible.

$\includegraphics[width=11cm]{pulssnubbercolor.eps}$

**Figure 1:** MBS3250 with puls snubber
$\includegraphics[width=11cm]{pulssnubber.eps}$

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Mads Clausen Institute

Organisation of the ESGI-47