Installation location of the unit displacement probe
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When installing shaft displacement probes on turbines, it is usually required that a fitter measure the shaft runout. I would like to ask whether half of this runout value also needs to be added to the interlock setting Conduct a survey: where should the shaft be positioned when an axis displacement probe is installed before the unit is started up?
There are two installation methods in our factory: 1. The fitter adjusts the alignment, and then the instrument is installed in the middle position. 2 The fitter determines whether it should be installed on the working side or the non-working side according to the unit operation manual, and then the fitter confirms the working side. Instrument adjustment probe.
After the fitter has made the installation, based on the backlash it has determined, the shaft is generally pushed to one side first, and then a displacement sensor is installed. Once installation is complete, it is advisable to push the shaft back to the other side in order to confirm that the mechanical backlash corresponds with the electrical signal. The interlock settings must be adjusted according to the specified values. The displacement amount is very important!
Our factory’s displacement probes come in two installation options: one at the midpoint and the other at the working end, depending on the specific settings of the secondary instrument.
Set the intermediate position to zero; for example, the zero point of a certain probe is -10V. After the fitter makes the installation, a serial value is provided to drive the shaft to a certain end; based on this serial value (displacement), the adjustment voltage is calculated, and then adjusted accordingly.
Determine the installation position of the displacement probe based on the position of the shaft; if the shaft is in the middle position, set the probe to output a linear voltage at that intermediate position； If the shaft is located at one end, the probe outputs the maximum or minimum voltage value depending on the direction of shaft movement.
1. Generally, they are installed on the shaft in the fan section, and the position of the shaft load is determined at the time of manufacturing; it is a device similar to a thrust plate, which we refer to as a displacement plate. The displacement of the shaft is measured by determining the distance between the displacement plate and the sensor. 2. The alarm values are also specified clearly at the time the fan is manufactured; typically, the alarm value corresponds to 50% of the full scale, while the shutdown value corresponds to 70% of the full scale
After the fitter completes the maintenance work, they will determine the position at which the shaft displacement of the mechanical assembly occurs – it can be either at the midpoint or at the working surface. It’s easy to figure out which position it is: by checking the interlock value; if the positive and negative values of this value are equal, then the displacement occurs at the midpoint, otherwise it’s at the working surface. The fitter is responsible for identifying the installation point based on the mechanical assembly parameters, and a displacement sensor is installed. After installation, the fitter is asked to adjust the parameters back and forth, and the instrument is used to determine the error (in my experience, it’s normal for there to be a discrepancy of around 30 units in the parameters, with the instrument indicating 26 units). In fact, the instrument also needs to take into account the mechanical assembly parameters.
The installation position of the unit’s displacement is determined during the unit’s design and production, and it cannot be changed arbitrarily. Each unit has its own fixed installation location for the displacement probe.
Generally, they are installed at one end of the non-drive shaft, such as those from Mitsubishi in Japan