DS200TCTLG1A | GE Mark VI Input Board

Description

Product Introduction (Anti-Template)

The DS200TCTLG1A is a high-density RTD input board—the board that converts RTD resistance signals into temperature values for turbine monitoring and control. This board gives you 16 RTD inputs in one VME slot, with per-channel excitation current, lead-wire compensation for 2-, 3-, and 4-wire RTDs, diagnostic LEDs per channel, and high accuracy.

The ‘TCTL’ in the part number indicates this is an RTD input board. The ‘A’ revision adds diagnostic LEDs per channel, improves accuracy, and adds better noise filtering. The board supports Pt100, Ni100, and Cu100 RTD types and provides per-channel excitation current (1mA constant current). Compared to using a general-purpose analog board with external RTD transmitters, the TCTLG1A gives you better accuracy, faster update, and integrated diagnostics.

Key Technical Specifications

Compatible Replacement Models

Replacement options depend on your channel count and accuracy requirements.

✅ Drop-in Replacement: The DS200TCTLG1 (no ‘A’) is a direct electrical drop-in—same pinout, same 16 inputs, same excitation. The differences: the base model has no diagnostic LEDs, lower accuracy, and a slower update rate. If you don’t need diagnostics and your accuracy requirements are moderate, the base model is a cheaper option (typically 15-20% less). The ‘A’ is the enhanced version.

⚠️ Software Compatible: The DS200TBSAG1A (6 RTD inputs, 16-bit) provides fewer channels with similar accuracy. Only use if you don’t need 16 channels.

⚠️ Software Compatible: The DS200TCCAG1A (analog inputs, 16-bit) provides analog inputs but no RTD excitation. You would need external RTD transmitters.

❌ Hardware Incompatible: Any thermocouple input board (TCTE series) uses different backplane pins and is not suitable for RTD signals.

Frequently Asked Questions (FAQ)

What’s the difference between RTD inputs and thermocouple inputs?

RTDs (Resistance Temperature Detectors) require a precision constant current source to measure resistance, and the resistance change is converted to temperature. Thermocouples generate a small voltage (millivolts) that changes with temperature—they don’t need excitation current. The TCTLG1A provides the 1mA excitation current for each of its 16 channels. You cannot plug an RTD into a thermocouple board—the excitation current would damage the thermocouple, and the signal levels are completely different.

How does lead-wire compensation work on this board?

The TCTLG1A supports 3-wire and 4-wire RTDs, which use additional leads to measure the resistance of the lead wires and subtract it from the total measurement. In 3-wire mode, the board measures the voltage across the RTD and the voltage drop in the two lead wires, then calculates the RTD resistance. In 4-wire mode, the board uses separate excitation and sense wires, giving the highest accuracy (no lead wire error at all). The board handles this automatically.

Can I use this board with a Mark VIe controller?

No—the TCTLG1A uses the older Mark VI backplane pinout. Mark VIe uses a different assignment and typically uses the IS200TCTLG1A for RTD inputs. Use the Mark VIe-specific board for new installations.

How do I test this board before installation?

Testing the TCTLG1A requires checking all 16 channels:

1. Visual inspection: Check for burnt components. Look for diagnostic LEDs.
2. Power-up test: Apply power. All diagnostic LEDs should briefly flash during POST.
3. Firmware check: Read firmware via ToolboxST—should be 3.0 or later.
4. Excitation current test: Measure the excitation current at each channel—should be 1mA ± 1%.
5. RTD simulation: Connect a 100Ω resistor (simulating 0°C for Pt100) to channel 1—read 0°C ± 0.2°C. Repeat for inputs 1-16.
6. Lead-wire compensation test: Connect a 3-wire RTD simulator and verify the compensation works correctly.
7. Diagnostic LED test: Disconnect an RTD—LED should flash amber or red.
8. Isolation test: Measure resistance between input channels—should be >10MΩ.

What’s the most common failure on this board?

Two issues specific to the RTD input design:

1. Excitation current source failure. The onboard 1mA current sources can fail due to voltage spikes—symptom: one channel reads an incorrect value.
2. Diagnostic LED failure. The LEDs can fail after 10+ years—a failed LED doesn’t affect the measurement.

If I’m using this board in a SIL-rated safety application, what’s the recommended maintenance interval?

The RTD inputs, per-channel excitation, and diagnostics make this board suitable for SIL-2 applications (not SIL-3). We recommend:

• Visual inspection: Every 6 months (check diagnostic LEDs)
• Power-up test: Every 12 months
• Excitation current test: Every 12 months
• Input accuracy check: Every 12 months (0.2°C spec)
• Isolation check: Every 2 years
• Full calibration: Every 5 years

What’s the lead time for a replacement TCTLG1A?

These boards are moderately available:

• New surplus: 2-4 weeks.
• Refurbished: 1-2 weeks. Ensure the refurbisher tests all 16 channels.
• Used/as-is: Available, but the excitation current sources are wear items.

Is there a direct Mark VIe equivalent?

Yes—the IS200TCTLG1A (Mark VIe version). The backplane pinout is different.

What termination board should I use with the TCTLG1A?

The TCTLG1A is designed to interface with the DS200TBSAG1A (RTD termination board) or the DS200TBSAG1 (RTD termination board). The termination board provides the terminal connections and the CJC sensors (if used). The TCTLG1A is the active board that provides the excitation current and measures the RTD resistance.

What’s the update rate for this board?

The TCTLG1A samples all 16 channels simultaneously at 20ms intervals—50Hz update rate.

What’s the maximum cable length for RTDs on this board?

GE recommends a maximum of 300 feet (100 meters) for 3-wire and 4-wire RTDs, and 100 feet (30 meters) for 2-wire RTDs. The limiting factor is the lead wire resistance relative to the RTD’s resistance. For 2-wire RTDs, keep cable runs as short as possible. The board’s 3-wire and 4-wire compensation handles longer cable runs effectively.

What RTD types does this board support?

The TCTLG1A supports Pt100 (100Ω at 0°C), Ni100 (100Ω at 0°C), and Cu100 (100Ω at 0°C). The RTD type is configured in software (ToolboxST) per channel. The board performs linearization based on the selected type. For the best accuracy, use Class A or better RTDs.

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