Turbine compressor

It should be “phase of the key”. Turbine key phase measurement involves installing a groove on the shaft under inspection, known as a key phase marker. When this groove moves to the probe position, it results in a sudden change in the distance between the probe and the surface being measured; the sensor then generates a pulse. One pulse is produced for each full rotation of the shaft, and the timing of these pulses indicates the position of the shaft during each rotation cycle. Therefore, by counting the pulses, the rotational speed of the shaft can be measured, and by comparing the pulses with the vibration signals of the shaft, the phase angle of the vibration can be determined, which is useful for dynamic balance analysis of the shaft as well as for fault analysis and diagnosis of equipment. The groove or ridge must be large enough so that the peak value of the generated pulse signal is not less than 5V (7V according to the AP1670 standard). Generally, when φ5 or φ8 probes are used, the width of such grooves or ridges should be greater than 7.6 mm, and their depth or height should be greater than 1.5 mm (2.5 mm or more is recommended); the length should be greater than 10.2 mm. The grooves or ridges should be parallel to the axis line, and their length should be as large as possible so that the probe can still face them even when the shaft moves axially. To prevent excessive changes in the gap between the probe and the surface being measured due to axial displacement, the key should be installed on the shaft in a radial position rather than an axial one. Install the key on the drive part of the probe as closely as possible, so that even if the drive part of the unit becomes disconnected from the load, the sensor will still output a keying signal. When the engine has different rotational speeds, multiple sets of keyboards and sensors are usually required to monitor it, so as to provide effective phase signals for various parts of the engine. The key phase mark can be a groove or a slot; when the mark is a groove, the initial installation clearance should be adjusted by aligning the probe with the entire length of the shaft (it is advisable to do this at the midpoint along the sensor), rather than by aligning it with the groove. And when the marker is a convex groove, the probe must have its initial installation clearance adjusted to match the top surface of the protrusion (it is advisable to install it at the midpoint along the sensor’s length), rather than being adjusted to match other flat surfaces on the shaft. Otherwise, when the shaft rotates, it may cause the protruding key to collide with the probe and cut it off.