IS220PRTDH1A Mark VIe | Replacement RTD Module for GE

Description

Product Introduction

The bearing temperature alarm was flickering—one second it was 85 °C, the next it was 92 °C, then back to 87 °C. The turbine wasn’t surging; the RTD module was. Swapped the IS220PRTDH1A with a spare, and the temperature reading locked onto 87.2 °C and stayed there. That’s what a healthy RTD module looks like.

GE’s IS220PRTDH1A is the dedicated RTD input module for the Mark VIe platform. Sixteen isolated channels, each designed to measure resistance from platinum (PT100), nickel (NI100), or copper (CU10) RTD elements. The module uses a 16-bit ADC with a 2.5 ms update rate per channel, giving you fast, accurate temperature data for bearings, exhaust gas, and inlet air. The H1A revision supports 2-wire and 3-wire RTD connections; the later H1B added 4-wire support for ultra-high accuracy applications. If you’re replacing an H1A with an H1B, be aware that the terminal block wiring is different—the 4-wire connections use additional pins. Check your wiring diagram against GEH-6721, Rev. M or later.

Key Technical Specifications

• Channel Count: 16 isolated RTD inputs
• Supported RTD Types: PT100 (α=0.00385), NI100, CU10 (software selectable)
• Wiring Configurations: 2-wire and 3-wire (4-wire available on H1B)
• Measurement Range: –200 to +850 °C (PT100); –60 to +250 °C (NI100)
• Resolution: 16 bits (0.01 °C typical)
• Accuracy: ±0.1% of reading + ±0.05 °C at 25 °C; ±0.25% over full temperature range
• Excitation Current: 1 mA (selectable to 0.5 mA for self-heating reduction)
• Update Rate: 2.5 ms per channel (all channels scanned sequentially)
• Isolation: 1500 VAC between field and logic; 500 VAC between channels
• Open Circuit Detection: Yes (flags channel if RTD resistance exceeds 400 Ω)
• Operating Temperature: –30 to +65 °C ambient

Quality Inspection Process (SOP Transparency)

Here’s the full test procedure for every IS220PRTDH1A before it ships:

Incoming Verification: The OEM packing slip is matched against the shipping manifest. Serial number enters GE’s warranty verification system to confirm factory-original distribution. Visual inspection includes checking the GE holographic label, verifying the 96-pin backplane connector is straight and gold-plated, and examining the PCB for any signs of rework. We also check the terminal block label—it must say “PRTDH1A” with correct markings.

Live Functional Test: The module installs in a Mark VIe test rack with a 24.0 VDC supply (Fluke 8845A). Power-on self-check: the status LED sequence should be amber → steady green. ToolboxST v8.0 verifies the module appears in the I/O tree and accepts a configuration download. We configure all 16 channels for PT100, 3-wire mode.

We connect precision resistance decade boxes (IET Labs HARS-LX) to each channel, simulating PT100 resistances at three calibration points: 100 Ω (0 °C), 138.5 Ω (100 °C), and 175.8 Ω (200 °C). For each point, we record the measured temperature in ToolboxST and compare to the calculated value. We also test 2-wire mode by connecting shorting bars to simulate lead wire resistance (0.5 Ω, 1.0 Ω) and measure the error.

For open-circuit detection, we disconnect the RTD leads and verify the module flags a channel fault within 500 ms. For the excitation current test, we measure the current through the RTD with a precision ammeter—it must be 1.00 mA ±0.5%.

Electrical Parameters: A Fluke 1587 megohmmeter measures isolation between each RTD channel and the logic circuit. We look for >20 MΩ at 500 VDC. Channel-to-channel isolation is verified at >10 MΩ. Ground continuity from the mounting screws to backplane ground is measured at <0.3 Ω.

Firmware Verification: Firmware version is read via ToolboxST. The PRTDH1A typically ships with v5.0 or later; we document the exact revision and upgrade if requested. All DIP switches are photographed and reset to factory default.

Final QC & Packaging: The QC report lists all 16 channels with their measured temperatures at the three calibration points, the 2-wire error test, the open-circuit test, the excitation current measurement, and the isolation measurements. The module goes into a new anti-static bag with a tamper-evident seal, then into a double-walled carton with foam inserts. A “QC Passed” label with the test date and technician’s ID goes on the outer box. All test data and photos are available on request.

Field Replacement Pitfalls

RTD modules are sensitive to wiring and grounding issues. Here’s my field-tested list.

Lead Wire Resistance
The PRTDH1A supports 2-wire and 3-wire RTD connections. In 2-wire mode, the lead wire resistance adds directly to the RTD resistance—100 Ω lead wire = 0.4 °C error per ohm (for PT100). A 10 Ω lead wire resistance gives a 4 °C error. I walked into a plant where the RTD leads were 100 meters of 24 AWG cable. The resistance was 6 Ω, and the bearing temperature was reading 2.4 °C high. The operator was about to shut down the turbine for a “hot bearing.” The fix was reconfiguring the module for 3-wire mode, which compensates for lead resistance. ❗ Use 3-wire connections for long runs. It’s a checkbox in ToolboxST. Don’t skip it.

Ground Loops
The PRTDH1A’s isolation is between field and logic, but it doesn’t isolate individual channels from each other. If you have multiple RTDs that are grounded at the sensor (many RTD probes have a grounded metal sheath), you can create ground loops between channels. I saw a plant where all 16 bearing RTDs had grounded sheaths, and the module’s readings were all over the place—the ground loop was injecting 60 Hz noise. The fix was isolating the sensor sheaths from ground with insulating washers. ❗ Ground loops will kill your accuracy. If your RTD probes are grounded, use a 4-wire connection (which isolates the sensing leads) or lift the ground at the sensor.

Excitation Current and Self-Heating
The PRTDH1A uses a 1 mA excitation current. For a PT100, that’s 0.1 mW of power dissipated in the sensor. For a small RTD (2 mm diameter), that’s enough to heat the sensor by 0.1–0.2 °C in stagnant air. In a gas turbine bearing housing, that’s fine—the oil flow carries away the heat. But if the RTD is in a stagnant air pocket (like an exhaust gas thermowell), the self-heating can be 0.5 °C. I had a plant where the exhaust temperature was consistently 0.4 °C higher than a thermocouple reference. The PRTDH1A’s excitation current was the culprit. The fix was reducing the excitation current to 0.5 mA (a software setting), which halved the self-heating. ❗ If your temperature readings seem consistently high, try the 0.5 mA excitation current. It’s a configurable option in ToolboxST.

Firmware and Calibration
The PRTDH1A’s accuracy depends on factory calibration coefficients stored in the module’s EEPROM. If you replace a module, the calibration coefficients are from the factory—they should be within spec. But if the module’s firmware is upgraded, the calibration coefficients may need to be reset. I’ve seen a plant upgrade the PRTDH1A’s firmware from v4.0 to v5.0, and the temperature readings shifted by 0.2 °C across all channels. The fix was re-entering the calibration values in ToolboxST. ❗ After a firmware upgrade, verify your temperature accuracy with a precision decade box. Don’t assume the calibration survived.

Channel Scanning and Update Rate
The PRTDH1A scans its 16 channels sequentially. Each channel takes 2.5 ms, so a full scan of all 16 channels takes 40 ms. That’s fine for bearing temperatures, which change slowly. But if you’re using a fast-responding RTD (like a thin-film probe on a bearing), a 40 ms delay is irrelevant. What’s relevant is the filter time—the module has a software configurable digital filter to reduce noise. The default is 100 ms, which adds a time constant to the signal. If you need fast response, set the filter to 0 ms. ❗ The filter is in ToolboxST. If your temperature readings are slow to respond to turbine startups, check the filter setting. Set it to 0 ms for fast transient response.

Get these five right and you’ll cut rework time by 90%.

New Original vs. Refurbished: Why It Matters

RTD modules are precision analog devices. Refurbishment carries significant risk.

New Original (New Surplus) means this unit came from GE’s production line, sealed in an ESD-safe bag. It has zero operating hours. The 16-bit ADCs are factory-calibrated against NIST-traceable resistance standards. The excitation current sources are trimmed to 1.000 mA ±0.1%. The serial number traces directly to GE’s production database. If a channel drifts out of spec, GE will provide a calibration certificate.

Refurbished risk: The ADCs in a refurbished module have been through thermal cycles, vibration, and aging. The reference voltage may have drifted—a 0.1% drift in the ADC reference becomes a 0.1% drift in temperature, or about 0.25 °C at 100 °C. A refurbisher can re-calibrate the module at room temperature, but the drift is often temperature-dependent. At 55 °C ambient, a refurbished module might be off by 0.5 °C. That’s enough to trigger a false bearing over-temperature alarm, causing a turbine trip. I’ve seen this happen in a combined-cycle plant. The refurbished PRTDH1A cost 600; the new surplus unit was 900. The false alarm cost the plant $20,000 in lost generation and the cost of an unnecessary inspection.

Real cost: A false high-temperature trip on a gas turbine is typically a full stop-and-inspect event—at least 8 hours of downtime. At 50/MWh for a 200 MW plant, that’s 80,000. The difference between refurbished and new surplus is negligible in comparison.

What we provide: We include a photo of the OEM packing slip with the GE part number and serial number. The anti-static bag is sealed with a tamper-evident label. We break the seal only for the QC test; if we do, we re-bag in a fresh anti-static bag with a new seal. The QC test report lists all 16 channels with their measured temperatures at three calibration points and the isolation measurements. You get a 12-month warranty.

Pricing context: Our price sits 30-50% above refurbished alternatives but 20-40% below GE’s current factory list price.

Performance Benchmarks & Test Results

Measured during our QC test. Conditions: test rack with a Mark VIe CPU, 24.0 VDC supply (Fluke 8845A), ambient 24 °C, firmware v7.2.

• Accuracy at 0 °C (100 Ω): Average error across 16 channels: +0.03 °C. Range: –0.02 to +0.08 °C. Within ±0.1% spec.
• Accuracy at 100 °C (138.5 Ω): Average error: +0.04 °C. Range: –0.03 to +0.09 °C.
• Accuracy at 200 °C (175.8 Ω): Average error: –0.02 °C. Range: –0.05 to +0.07 °C.
• 2-Wire Error: With 1.0 Ω lead resistance (simulating 5 meters of 24 AWG cable), the 2-wire measurement showed a +0.4 °C error. The 3-wire measurement with the same lead resistance showed a +0.01 °C error. ❗ Use 3-wire for accuracy.
• Excitation Current: Measured at 1.001 mA average across all channels (range: 0.998–1.003 mA). Within ±0.5% spec.
• Update Rate: 2.5 ms per channel. Full scan: 40 ms.
• Thermal Performance: After 1 hour of continuous operation at 25 °C ambient, the module’s PCB temperature stabilized at 30 °C above ambient (55 °C at 25 °C). The accuracy at that temperature drift was measured at ±0.18%—within the ±0.25% full-temperature specification.
• Open Circuit Detection: The module flagged a fault within 400 ms of the RTD leads being disconnected.
• Isolation Resistance (Channel to Logic): Measured 25 MΩ at 500 VDC—well above the 10 MΩ minimum.
• MTBF (Published): GE’s datasheet lists 165,000 hours at 40 °C for the PRTDH1A. Based on field data, expect 12-14 years of service under normal conditions.

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