The Mark V is a triple modular redundant (TMR) control system for industrial gas and steam turbines. Its boards are not scattered at random — each one belongs to a specific core, and the four-letter acronym in the middle of the DS200 part number tells you which.
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The core layout, in plain terms
A Mark V panel is organised into cores, and the redundancy that gives the system its reliability lives in this arrangement:
- <R>, <S>, <T> — the three control cores. This is the "triple" in triple modular redundant. Each runs the same control logic on its own hardware, and the three results are voted. A board that exists in R also exists in S and T.
- <Q> — the I/O cores, seen as <Q11> and <Q51>. Digital I/O and relay output boards live here.
- <C> — the communications and interface core.
The practical consequence for procurement: when an R-core board fails, you are usually buying one card, but you should ask whether the S and T cores hold the same revision. Mismatched revisions across a voted set are a classic source of intermittent trips.
The board acronyms
TCQA — analog I/O
The main analog I/O card in each of the <R>, <S> and <T> cores, sitting in position 2. It sits in a daisy-chain with the STCA and TCQE boards. If you are replacing analog inputs on a Mark V, this is the card you are looking at. Example on our shelf: DS200TCQAG1B / DS200TCQAG1BED.
TCQC — the overflow companion
Where the analog channel count exceeds what a TCQA can carry, the TCQC picks up the overflow and sits in the chain ahead of the TCEA boards. See DS200TCQCG1A / DS200TCQCG1ADB.
TCDA — digital I/O
Found in the digital I/O cores <Q11> and <Q51>. It processes output signals coming from the two TCRA boards and input signals coming from the DTBB and DTBA terminal boards, and passes them across the IONET.
TCEA — emergency / protection chain
The TCEA boards are linked in a daisy chain (TCQC → TCE1 → TCE2 → TCE3 → TCDA) and are commonly designated TCEA-X, TCEA-Y and TCEA-Z. Because they sit in the protection path, revision matching matters more here than almost anywhere else in the panel.
TCRA — relay output
The relay output board, used in the <Q11> and <Q51> cores. A TCRA carries thirty relays, labelled K1 through K30. If you are chasing a dead solenoid or a contact that will not pick up, this is the board in the path. Example: DS200TCRAG1A / DS200TCRAG1AAA.
UCPB — CPU daughterboard carrier
The UCPB provides the connectors required for mounting the CPU daughter board, and mounts on the R-core motherboard. Signals read on the STCA boards are conditioned and written to the I/O engine on the UCPB via bus connectors J1 and J3. Example: DS200UCPBG6A / DS200UCPBG6AFB.
STCA — ARCNET LAN driver
The STCA is the LAN driver board and the head of the STCA → TCQA → TCQE chain. IONET, the internal Mark V panel network, is what carries data between the STCA, the TCDA boards and the TCEA boards.
CSSA — cell state sensor
Monitors cell state within the panel. See DS200CSSAG1A / DS200CSSAG1AAA.
GDPA — gate driver
Drives the power gates in the drive section. See DS200GDPAG1A / DS200GDPAG1AFB.
Terminal boards vs. control boards
DS200 numbers beginning DTB (DTBA, DTBB, DTBC, DTBD) are terminal boards — the field-wiring landing points, not the processing cards. They fail far less often than the control cards, but when they do, the failure looks identical from the HMI. Before you condemn a TCDA, check the terminal board feeding it.
Diagnosing before you order
- Does the fault follow the core or the signal? If R alone reports the fault and S and T agree with each other, the board in R is the suspect. If all three cores see it, look at the terminal board or the field device.
- Is the revision the same across R, S and T? Pull the numbers off all three before ordering.
- Is the board actually in the path? The daisy-chain layout means an upstream board can present as a downstream failure. A dead STCA can look like a TCQA problem.
Requesting a quote
Send us the full part number including the revision tail, the core the board sits in, and the revisions currently fitted in the other two cores. Tell us whether you can accept a superseding revision — for out-of-production Mark V cards this is often the difference between shipping this week and waiting months. We reply within 24 hours, ship worldwide DDP, and accept purchase orders.