Hi,

we have an RTD that goes to a high temperature and trips the machine. When disconnected and measured, the resistance represents the normal temperature. when reconnected to the input, the Mark 5 shows the normal temperature. We suspect the input, has anyone experienced this before? we are considering moving the wires to a spare input and readressing the program to it.

Thanks for any help.

 

davidmcc,

RTD wiring for Speedtronic turbine control panels is ALWAYS something of an issue (due to the way GE usually wired them when they supplied the turbine-generator package--which was to use two-wire, twisted, shielded cables instead of three-wire, twisted, shielded cables). I suspect, thought, that EGT used three-wire cables for these signals.

It's still possible that there's a loose connection or termination somewhere in the loop that's causing a problem, and hopefully you've ruled that out already.

Yes; you can re-assign the input in IO.ASG, change the I/O Configuration to enable the spare input and scale it properly, and disable the original input. Then you would just have to run MK5MAKE.BAT to get the new address for signal name into the CSP segment file and into the "Global Data Dictionary" (UNITDATA.DAT), then download the CSP and IOCFG segments to <C> and <Q> and re-boot the Mark V processors one at a time, waiting a couple of minutes between re-boots, and then re-boot the <I> or HMI to get the new information into the operator interface RAM. I don't think you will have to do anything with the CIMPLICITY project if you have GE Mark V HMIs (using MS-Windows and CIMPLICITY), but I could be wrong about that....

 

Hi CSA,

Thanks for your reply, we just got the outage today for two weeks for boroscope, so we want to resolve the RTD fault also. It is the gearbox drain oil temperature, you're right it is a 3 wire system on EGT. We found the wires at the Mark V and at the A520 termination section in the TCC, but we have no idea about where the RTD is physically located and if there is a local marshaling box - would you have any guidance on this?

p.s. we have Mark 5 studio and cimplicity on a PC rather than an <I>.

thanks for your help.

Regards,
David

 

DavidMCC,

I'm sure there's a local JB, and the RTD is likely mounted in the L.O. Drain line from the Reduction (Load) Gear. I'm not that familiar with the gearboxes used by EGT (Flanders?) and I'm not sure where to find the drain line, but I'm sure you will find a JB somewhere either on the gearbox housing or somewhere outside the Load Gear Compartment where low-level signals, including this RTD, are located. A lot of times, packagers used dual-element RTDs, and only connected one of them to the turbine control system, so you might find a second, "spare" RTD wired out to the local JB and you could just swap over the interconnecting wiring.

EGT may even have already connected the second, "spare" element to the marshaling cabinet for you. If you have drawings for the marshaling cabinet, and interconnecting wiring drawings, they may show this is already done.

I have successfully used a simple potentiometer to simulate an RTD input to the Mark V. One can't use one of the new-fangled electronic RTD simulators because digital Speedtronic turbine control panels multiplex the RTD inputs--meaning they don't read the input continuously and that frustrates the new-fangled electronic RTD simulators. You could also just connect a known good working RTD from another input to the Mark V to the non-working input to see if the Mark V input is working correctly (temporarily).

Please write back to let us know how you fare!

 

Hi CSA,

Just to follow up on the RTD fault, we found that the probe on the RTD had been bent as a shortcut to ease installation/removal. When replaced it worked ok. It did pass through a junction box from memory.

Regards,
David

 

davidmcc,

Thank you so much for the feedback! It's very helpful to a lot of people who follow these threads--now and in the future.