Have GW Lisk LVDT's installed on turbine gas valves connected to Mk6 controller and finding that;

1) The minimum voltage feedback when the LVDT is fully retracted is 1.1vac and 4.0vac when fully extended - this is with LVDT's removed from valve and connected directly to mk6

2) When the valve is given 50% reference the actual movement is only about 35% - approx 7% actual movement seen for each 10% reference. Beyond this position the actual step size increases for each 10% reference increase.

3) When the LVDT is connected directly to the mk6 and piston inserted and retracted by hand the second half of the LVDT movement sees a reduction of change in voltage feedback 0% = 1.1v, 25% = 2.1v, 50% = 3.0v, 75% = 3.55v, 100% = 4.0v

4) Have found that internally to the LVDT there is no direct connection between the excitation coil and feedback coil - this is unusual to me since on other LVDTs I have seen on mk5/6, there is a direc6t internal connection - Shaevitz and Kavlico LVDTs.

Wondering if anyone experienced problems with GW Lisk LVDT's on mk5/mk6 controllers before and was there a solution ?

Thanks in advance.

 

mogy,

What does GE say about this?

And why would the type of Speedtronic panel make a difference with the LVDT feedback?

As you know, most of the LVDTs used on GE-design heavy duty gas turbines are to be set for a zero-stroke voltage of 0.700 VAC RMS and the range of travel should not result in a maximum output voltage of more than 3.500 VAC RMS for linear feedback. In other words, the LVDTs normally used should be adjusted such that the linear output range should be between 0.700 VAC RMS and 3.500 VAC RMS for the expected stroke of the actuator or device to which the LVDTs are attached.

Have you verified with GE what the zero-stroke voltage for this manufacturer's LVDT is, and what the range of linear output voltage should be?

 

I mostly think about bad wiring, part of the primary of LVDT is also in the secondary Red black for primary (Kavlico and sentech) and blue yellow for secondary and the yellow is in fact partialy took from the primary coil (but you cannot check this from outside) and I am also surprise by this "high" voltage of 1.1 and 4Vac it should be more around 0.7 and 3.5 Vac as per other response

pascal
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