In Mark V Control Sequence Document SEQ_TRB1.SRC, Rung no.4, it is given that when TNH less than or equal to a particular value (True), say 'B ', L14HR will get command. When TNH greater than or equal to another value (False), say 'C', L14HR will drop.

My question is what command will go to L14HR when TNH is between B and C? Or is the whole logic wrongly understood by me?

 

14HR will become TRUE on decreasing speed when the shaft speed drops below setpoint 'B' and will become FALSE on increasing speed when the shaft speed exceeds setpoint 'C'. So the answer to your question is the value between 'B' and 'C' is whatever it was before it enter this speed range. I.e., on speed decreasing from above 'C' it will be FALSE; on speed increasing from below 'B' it will be TRUE.

 

Thank you very much...

 

But in control sequence document point 'B' is named as pick up point, but you say it comes into picture when turbine speed drops below that point. Same is the case with point 'C', point 'C' is named as drop out point. How is it possible ?

 

L14HR, when a logic "1", means that the turbine shaft is "at Rest", or, at zero speed.

"Pickup" is another term for TRUE or logic "1". "Dropout" is another term for FALSE or logic "0".

So, when TNH is less than TNK14HR1, L14HR becomes a logic "1", or "picks up". When TNH is greater than TNK14HR2, then L14HR becomes a logic "0", or "drops out".

This comparator in this particular speed sensor in the 'L14TV1 - Speed Logic Sensing' block is the opposite of all the other comparators in the block. All the other comparators pick when TNH is greater than the "B" input, and drop out when TNH is less than the "C" input.

A lot of people complain because the value(s) of TNK14HR1 (and -2) is(are) above zero RPM. That's because it's very difficult for passive speed pickup circuitry to determine exactly when the shaft speed is at 0 RPM. So, the value for "zero speed" (TNK14HR1) is usually some very low number, like 0.06% speed, which for a machine rated at 5100 RPM is approximately 3 RPM, and the value for drop-out (TNK14HR2) is something like 0.31% (approx. 16 RPM). So, DON'T change these values! Or, it's likely the unit won't behave like it should, and that wouldn't be the fault of the Control Constant value(s)....

 

Just a little history on some of these terms:

"Pickup" and "Dropout" originated in the days of electromechanical relays (Mark I and Mark II Speedtronic control). The 14HR speed relay picked up (energized) at (almost) zero speed and dropped out (de-energized) when the shaft was above zero speed. L14HR is the logic equivalent signal in digital controls.

The "R" in 14HR came from the word ratchet, not rest. When 14HR picked up, it was safe to engage the ratchet to rotate the shaft. Having the relay pick up was considered the fail safe mode (safe for the ratchet mechanism).

So, the 14HR speed relay works opposite to the other speed relays in that it is energized at low speed and de-energized at higher speeds.

 

History is a good thing!

Thanks!

 

Great deal of information.....
Thankyou all.....

 

Hey...can anyone plz mail me the control sequence manual and specifications manual of MarkV...

please mail at eury.tarun [at] gmail.com