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Bestech releases signal conditioners for gas turbine LVDTs and PG LVDT for steam turbine valves

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Bestech Australia announces the availability of S1A signal conditioners from Alliance Sensors.

The S1A DIN rail module is specially designed to overcome the difficulties of AC-LVDT setup and set zero/full scale by simply using the front panel pushbuttons and reading via a built-in null indicator. The S1A signal conditioner is used to solve multi-channel LVDT measurement system subject to heterodyning, or ‘beating’ between channels (crosstalk), which is a mutual interference phenomenon that occurs when LVDT signal cables are bundled together or laid close to each other in a wire trough resulting in a very low frequency signal as a repetitive drift with a period of many seconds.

This problem is typically solved in multiple channel systems by creating a ‘master’ oscillator using the oscillator from one of the signal conditioners to supply the same excitation frequency to all of the LVDTs. The oscillators in the other LVDT signal conditioners are overridden by the master and considered ‘slaves’. The idea is that there cannot be any beat frequency interference if all the LVDTs are operating at the exact same frequency. This method works quite well but has a major drawback as the redundant system is no longer fully redundant. 

The system is now dependent on one oscillator in one signal conditioner to supply all the LVDTs with the proper excitation frequency. If the master fails, either the other channels stop operating, or they revert to their original oscillator frequencies and the multiple channel DC outputs now display beat-frequency-produced noise, ripple, or output drifting. Many companies offer LVDT signal conditioners with a master/slave function, but they all are fully susceptible to the beat frequency problem if the designated master oscillator falters or fails.

To solve this beat frequency problem with multiple LVDT installations, the S1A offers a choice of four excitation frequencies and eight analogue DC outputs, as well as an RS-485 digital communications port. 

The PG Series linear sensor is the first LVDT-based valve position sensor engineered specifically for applications in electric power generating steam turbine control systems and other heavy duty linear position measurements.

The PG Series includes PGHD Heavy Duty LVDT, the PGSD Super Duty LVDT, and the PGRR mild Radiation Resistant super duty LVDT. PG Series sensors are available in full ranges from 25.4mm to 381mm with operating temperature up to 175°C.

Unlike typical AC-LVDT sensors used for valve position sensing on steam turbines that were never really designed for physically demanding use, the PG Series heavy duty linear sensors can withstand tough use, providing a new level of reliability at comparable costs. 

Key features of the PG Series include a wire connection terminal block inside an IP-68 sealed housing; 3/8 inch diameter core rod securely encasing the LVDT’s core; in-line ball joint on the connecting rod to manage installation misalignment; double contact shaft seal keeping dirt and grit out; electrical connections with Euro-style screw-clamp-type terminals accepting No. 24 to No. 14 AWG, eliminating the nuisance of soldering to connectors; a 3/4-NPS female hub accepting liquid tight connectors, cord grips, or flexible conduit fittings; and a 2-year warranty. 

The PG LVDTs are ideal for use in interceptor valves, governor valves, throttle valves, bypass valves, and stop valves. 

The PG series LVDTs bring a new level of reliability in the extreme environment of steam turbine deck applications.

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