MK4 Fire Detection

C

Thread Starter

cactus_chris

I started looking for the cause of L45FT2 during a startup. I figured it was a single detector "on" (45FT-9B), but it stays in during both states of L45F1X, which seems odd. Thats when I noticed L45F1X momentarily dropping to 0 during its 60 minute on cycle, despite L45FZ1 being solidly on.. Any ideas?
 
cactus_chris,

When a fire detector (Fenwal switch) is closed, it will be closed regardless of the polarity of the voltage applied to it. Changing the polarity of the applied voltage was a way of using the Mark IV contact inputs circuitry to detect the closure of a single fire detector, so as to alert the operator/technician to the closure of a single fire detector which might happen because a fire is beginning or because a single fire detector has been damaged (usually by a mechanic/pipefitter crawling around are dropping pipes/tools on the fire detector, but sometimes they do just fail after some period of time especially if they haven't been tested properly).

So, a failed/closed fire detector will always be closed; it only just alarms every other hour when the polarity changes.

I don't have a Mark IV Speedtronic elementary to refer to at this time, but your second question isn't really clear. If the relay isn't remaining energized during the 60 minutes when it's supposed to be energized, that's one indicator of a failing coil circuit, or a failing relay driver of the Mark IV. Since these relays are the most "active" in the Mark IV (changing state every hour, regardless of whether the unit is running or not) they will likely fail more often than any other, and the failure mode will be coil or coil spring related, not current through the contacts when there is no fire.

Hope this helps!
 
C

cactus_chris

Thanks again for replying. I was being too brief.

I was initially responding to L30A229. L45FT2 is staying a "1" constantly, and not going away every other hour. My understanding was similar to what you stated, so I was expecting to either see the trouble alarm going in and out, or the fire alarm and trip. That was the first thing that confused me. So I started to look at the 45F1X relay...

The second thing that confused me occurred once I started digging into the logic that cycles the 45F1X. There are 3 simple rungs on the bottom of my Elementary Page 16C:

LDF L45FZ1
ESC TMV K45FZ T45FZ (60 MIN)
STO L45FZ

LD LD45FZ
ESC TMV K45FZ1 T45FZ1 (60 MIN)
STO L45FZ1

LD L45FZ
STO L45F1X (DRIVES 45F1X/4R8EC[49K])

On Data List 16 I have L45FZ, L45FZ1, and L45F1X.

at t=0 through t=60

L45FZ1 = 0
L45FZ = 0
L45F1X = 0

at t=60 through t = 120

L45FZ1 = 0
L45FZ = 1
L45F1X = 1

But then I started to see L45F1X go to zero independent of L45FZ1. I first saw it on a trend on my aftermarket HMI. I second guessed it, but then I started to see the momentary L45F1X zeros on Data List 16 too. How is that possible given that:

LD L45FZ
STO L45F1X

is in the C computer?

I don't see the cycling on Data List 13.

This started during an outage, with no real maintenance done on this turbine or controls. The turbine is now running with the trouble alarm.

I'm not sure that the two problems are related. I'm really stumped by the second problem. The first problem could still be a bad relay, I suppose.
 
C

cactus_chris

>But then I started to see L45F1X go to zero independent of L45FZ1.<

CORRECTION:
I've said this twice, in error, and I'm not sure why. I keep meaning to say:

L45F1X go to zero independent of L45FZ.
 
cactus_chris,

I believe the two problems are unrelated--other than they're both related to the fire protection system....

You should be able to visually observe the voltage-switching relays change state; older relays had the red LED to indicate when energized. A lot of the relays used for replacement did not. I have used original equipment relays which were "spare" (not used for a particular purpose) as replacements to make use of the red LED. (Just make sure the relay you are moving has the same coil rating--some of the relays have 28 VDC coils, and others are 125 VDC coils. I believe the fire protection relays used 125 VDC coils.)

As for the changes-of-state, I don't believe the physical relays in a Mark IV are monitored for actual physical state (other than possibly monitoring current flow--which I don't recall being the case, but it's been a LONG time since I've looked at a Mark IV MaxCase elementary). My best guess would be what you're seeing on the third-party HMI is likely some glitch in communications if you're not seeing it on Data List 13, but that's just a SWAG (Scientific Wild-Arsed Guess). Again, you should be able to monitor the relays visually to see if they're actually changing state. You could change the time between changes to a couple of minutes so you don't have to return every hour (changing at one-hour intervals was just a convenient decision--nothing else relies on that specific period).

Hope this helps!
 
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