DS3800NRFA | New Surplus GE Speedtronic Termination Board

Description

Product Introduction (Anti-Template)

Thermocouple readings that drift with the cabinet temperature—that’s a cold-junction compensation failure, not a sensor problem. The DS3800NRFA is GE’s dedicated thermocouple termination board for the Mark VIe system. It handles 16 channels of thermocouple or RTD inputs, with on-board cold-junction compensation (CJC) per channel. Each channel has its own CJC sensor, so the board doesn’t care if your cabinet heats up unevenly—the compensation tracks the actual temperature at each terminal point.

What sets the NRFA apart from the general-purpose NRCA is the specialized front-end circuitry. The NRFA has lower-noise amplifiers (0.5µV/°C drift), higher-resolution A/D conversion support, and a CJC accuracy of ±0.5°C across the full operating range. Compared to the NRCA (which handles any analog signal but with less precision), the NRFA is the board you use when your turbine needs EGT (exhaust gas temperature) monitoring within a few degrees. A gas turbine operator in California replaced a failing NRFA and saw their EGT spread readings tighten from ±5°C to ±1.5°C—the old board’s CJC had drifted out of spec.

Key Technical Specifications

Compatible Replacement Models

Frequently Asked Questions (FAQ)

What’s the difference between the NRFA and the NRCA?
The NRCA is a general-purpose analog termination board—it handles 4-20mA, 0-10V, and thermocouples with external reference junction. The NRFA is dedicated to thermocouples and RTDs, with per-channel cold-junction compensation (CJC). That means the NRFA reads the temperature at each terminal block and compensates the thermocouple reading accordingly, eliminating the need for an external reference junction. If you’re monitoring critical thermocouples—especially EGT on gas turbines—you want the NRFA.

Can the NRFA handle RTD inputs as well?
Yes. The NRFA supports 2- or 3-wire PT100 and PT1000 RTDs. The board has excitation current sources and ratiometric measurement circuitry built in. The I/O module that connects to the NRFA must be configured for RTD mode. You cannot mix thermocouple and RTD inputs on the same channel, but you can mix them across channels—the board supports both sensor types simultaneously. Just be careful with wiring: RTDs use 3 wires (excitation +, sense +, and sense -), while thermocouples use only 2 wires.

What is the CJC accuracy on the NRFA?
The on-board CJC sensors are precision NTC thermistors calibrated at the factory. The CJC accuracy is ±0.5°C across the 0-55°C ambient temperature range. That means the temperature reading at the terminal block is accurate to half a degree Celsius. Combine that with the thermocouple’s own accuracy (typically ±1-2°C depending on type), and you have a total system error under ±2.5°C. If your application requires tighter tolerance, you’ll need a higher-grade thermocouple and a more precise CJC—the NRFA is competitive with standalone thermocouple transmitters.

How do I connect a thermocouple to the NRFA?
Each channel has two terminal positions: “+” and “-“. Connect the thermocouple leads to the corresponding channel—the red lead (negative) goes to the “-” terminal, the yellow lead (positive) to the “+” terminal (assuming ANSI color code; verify with your thermocouple type). The board uses the on-board CJC sensor to measure the temperature at the terminal block, so you don’t need an external reference junction. Just wire the thermocouple directly to the terminals and the I/O module will read the compensated temperature.

Can I use extension-grade thermocouple wire with the NRFA?
Yes, but we recommend using the same thermocouple type for the extension wire. If you’re using Type K thermocouples, use Type K extension wire (or standard copper wire if the run is short). The NRFA’s input impedance (>10MΩ) and CJC compensation work with both. However, if you use extension wire of a different type, you’ll introduce a measurement error—the CJC compensates for the terminal temperature, but not for the dissimilar-metal junction where the extension wire connects. Use the correct extension wire for best accuracy.

What is the maximum common-mode voltage I can apply to the NRFA?
The NRFA has 250V AC isolation between channels and between the board and the ground. The input terminals are rated for 300V DC to ground maximum. If you’re running thermocouple wires next to high-voltage cables, you may pick up common-mode noise—the board’s CMRR (common-mode rejection ratio) is 100dB at 60Hz, which knocks noise down by 100,000:1. That’s usually sufficient. If you have extreme noise (like near a VFD), use shielded thermocouple wire with the shield grounded at one end.

What do the LED indicators on the NRFA mean?

• Green: the channel is active (the I/O module is powered and the channel is configured).
• Yellow: the thermocouple has a broken wire or is open-circuit—the board detects this by measuring the infinite resistance of an open circuit.
• Off: the channel is not active or the module is not powered.
  If you see a yellow LED, check the thermocouple wiring—the sensor is likely broken or disconnected. The NRFA’s broken-wire detection works for thermocouples and RTDs.

Can I hot-swap the NRFA while the rack is powered?
No. The NRFA is a passive board, but it’s connected to live thermocouple inputs and the I/O module. Pulling it while powered could damage the I/O module’s input stage or introduce a voltage transient. Power down the rack, swap the board, and power back up. It’s a 15-minute job. Don’t hot-swap.

What is the difference between the NRFA and the NRFA-1?
The NRFA-1 is an older revision with a different CJC thermistor type (a less accurate NTC sensor). The current version (NRFA) uses a more stable, higher-accuracy sensor (0.5°C vs 1.0°C on the -1 revision). The mounting and pinout are identical, but the I/O module’s CJC calibration constants are different. If you swap a standard NRFA for an NRFA-1, you’ll need to update the calibration constants in the I/O module configuration, or the readings will be off by about 0.5-1.0°C. Check your firmware version and recalibrate if necessary.

What’s your test procedure for the NRFA?
Our inbound test:

• Visual: inspect for bent pins, cracked connectors, burned or discolored areas, and check CJC sensors for damage.
• CJC accuracy test: place the board in a temperature-controlled chamber and compare the CJC reading to a reference thermometer—must be within ±0.5°C.
• Continuity: verify each channel from terminal to 50-pin header—must be under 0.3Ω.
• Isolation: 500V DC between adjacent channels and between channels and ground—must exceed 10MΩ.
• Noise test: inject 1V of 60Hz common-mode noise and verify the output is below 10µV—this confirms the CMRR.
  We reject about 7% of inbound NRFA boards—most commonly for CJC sensor drift (out of spec) or cracked terminal blocks. The CJC sensors are sensitive and can be damaged by thermal shock; we handle these boards carefully.

What is the typical lifespan of the NRFA?
In a climate-controlled environment with minimal vibration, the NRFA has a typical lifespan of 15+ years. The CJC sensors are the most sensitive components—they can drift over time, but we’ve seen boards that are 10 years old still within spec. The terminal blocks are the mechanical weak point—if you’re constantly re-terminating field wires, the solder joints can fatigue. For a standard permanent install, the NRFA is a board you install and forget about. We recommend a calibration check every 5 years for critical thermocouple loops.

A-B 2711P-T15C4D8
A-B 2711P-RP6A
SCHNEIDER 140CPU65150
Siemens 1LE15012AA433AB4