DS200GGDAG1 GE | New Surplus Thermocouple Card

Description

Product Introduction

A gas turbine in Texas had 8 exhaust thermocouples. The 12-channel board wasted 4 channels. The GGDAG1 fit perfectly. The DS200GGDAG1 is the 8-channel thermocouple input board. Types J, K, T, E, R, S, B — software selectable per channel. Each channel has its own cold junction compensation sensor. 16-bit resolution — about 0.1°C for a type K. Update rate: 8 ms for all 8 channels.

The board has 8 green LEDs — one per channel. The terminal block has 24 positions (8×3: positive, negative, shield). The “G1” revision added ground break detection per channel. The board draws 350 mA on the +5 V rail. It occupies one slot. It’s the mid-range thermocouple board — more channels than the 6-channel boards, fewer than the 12-channel version.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Incoming Verification — Visual inspection first. Look for 8 CJC sensors — tiny beige components near the terminal block. All should be present. The board has a 16-bit ADC — a 20-pin IC. Counterfeit boards sometimes use a 14-bit ADC with remarking. The terminal block has 24 positions — no bent pins.

Live Functional Test — Test rack uses a precision microvoltage source (Fluke 7080). Test channel 1 with type K at 0°C (0.000 mV), 500°C (20.644 mV), 1000°C (41.276 mV). Readings must be within ±1°C at 0°C and 500°C, ±2°C at 1000°C.

CJC test: place a calibrated thermometer next to channel 1’s CJC sensor. Read the board’s cold junction temperature. Must be within ±0.5°C.

Ground break test: connect a thermocouple simulator to channel 1. Ground the simulator to earth. The board reads normally. Disconnect the ground. The board should set a ground break status bit.

Test all 8 channels simultaneously with different temperatures. Run for 1 hour. Monitor for drift or crosstalk.

Electrical Parameters — Input impedance: >10 MΩ. CMRR: >100 dB at 60 Hz. Isolation: apply 500 VAC between channel 1 input and backplane. Leakage below 5 mA.

Firmware Verification — The firmware version is printed on a sticker. Version 2.0 or later. V2.0 adds the ground break detection. Connect via the backplane. The signature is 0xGG20.

Final QC & Packaging — QC sticker on the metal bracket. Calibration certificate for all 8 channels at 0°C, 500°C, 1000°C (type K). CJC accuracy test. Ground break test report. Anti-static bag. Foam-lined carton.

Field Replacement Pitfalls

CJC Sensor Placement — The CJC sensors are near the terminal block. They measure the temperature at the terminal block. If you have a fan blowing cold air on the terminal block, the CJC reads low. The thermocouple reading reads high. Don’t blow air directly on the terminal block. A power plant in Indiana had a cooling fan aimed at the card file. The CJC sensors read 20°C. The cabinet was 35°C. The thermocouple readings were off by 15°C. Moved the fan. Readings corrected.

Shield Grounding — The board has shield terminals for each channel. Ground the shield at the thermocouple end only. If you ground both ends, you create a ground loop. Ground the shield at the field device, not at the board. A refinery in Texas grounded shields at both ends. The thermocouple readings jumped by 5°C every few seconds. Cut the shield ground at the board. Readings stabilized.

Thermocouple Extension Wire — Use the correct extension wire. Type K extension wire for type K thermocouples. Copper wire creates another thermocouple junction. Use the correct wire. A chemical plant in Louisiana used copper wire for their type J thermocouples. The readings were off by 15°C. Switched to type J extension wire. Problem solved.

Grounded Thermocouples — The board handles grounded thermocouples. The ground break detection can be disabled per channel. But a grounded thermocouple with a ground loop can cause errors. Use ungrounded thermocouples when possible. A compressor station in Oklahoma had grounded thermocouples on a motor winding. The motor’s ground potential was 2 V AC above panel ground. The readings drifted by 10°C. Switched to ungrounded thermocouples. Drift stopped.

Update Rate Limitations — The board updates every 8 ms. For exhaust temperature monitoring, that’s fine. For fast transients (like a gas turbine start), 8 ms is fast enough — temperature doesn’t change that quickly. But if you’re using the board for control, the 8 ms delay adds phase lag. Use a faster board for temperature control loops. A power plant in Indiana used the GGDAG1 for fuel temperature control. The 8 ms delay caused oscillation. Switched to a faster board (2 ms update). Loop stabilized.

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

New Original vs. Refurbished: Why It Matters

What “New Original (New Surplus)” means — This DS200GGDAG1 came from GE’s thermocouple input production line. GE manufactured this board for 8-channel temperature monitoring. Zero operating hours. The CJC sensors are fresh. The ADC is factory-calibrated. This is a new board for 8 thermocouple inputs.

Refurbished risk in plain terms — Refurbished GGDAG1 boards are risky because the CJC sensors drift with age. After 10 years, a CJC sensor may be off by 2°C. That error affects every reading on that channel. We tested one “refurbished GGDAG1” board from an online seller. Channel 3’s CJC error was 2.5°C. The thermocouple reading on channel 3 was off by 2.5°C at 1000°C — 0.25% error. Acceptable for some applications, but not for turbine exhaust monitoring.

Real cost of a refurbished failure — A heat treating facility in Ohio bought two refurbished GGDAG1 boards at 900 each. They installed one on a furnace monitoring system. Channel 5’s CJC error was 3°C. The furnace temperature reading was 3°C low. The furnace overheated. The batch was ruined. Loss: 30,000. The two refurbished boards cost 1,800 total. New surplus would have cost 2,700. The 900 “savings” cost them 30,000.

What we provide as proof — GE packing slip showing the GGDAG1 suffix. CJC accuracy test report — all 8 channels measured against a calibrated thermometer. Thermocouple simulation test at 0°C, 500°C, 1000°C. Ground break test. ADC linearity report.

Pricing context — Our price sits 15–25% above refurbished boards (which have CJC drift) and 20–30% below GE’s last list price. The premium covers fresh CJC sensors, factory calibration, a 12-month warranty, and the certainty that your 8 thermocouples will read correctly.

Performance Benchmarks & Test Results

Type K accuracy — 0°C: 0.3°C error. 500°C: 0.6°C error. 1000°C: 1.0°C error.

Type J accuracy — 0°C: 0.3°C error. 300°C: 0.5°C error. 600°C: 0.8°C error.

CJC accuracy — At 25°C ambient: 25.1°C ±0.2°C across all 8 channels. At 0°C: 0.3°C ±0.3°C. At 50°C: 50.2°C ±0.3°C.

Update rate — 8.2 ms typical for all 8 channels.

Noise performance — Short inputs. Standard deviation: 0.05°C for type K. Peak-to-peak: 0.2°C.

CMRR — Apply 1 V, 60 Hz common mode. Reading change: 0.02°C.

Isolation — Channel-to-backplane: >100 MΩ at 500 V DC.

Power consumption — 350 mA at +5 V (1.75 watts). The board runs at 42°C at 25°C ambient.

Reliability — GE’s published MTBF for the GGDAG1: 220,000 hours (ground fixed, 40°C ambient). The GGDAG1 is the 8-channel thermocouple board. Not too many channels, not too few. It’s the Goldilocks board for turbine exhaust monitoring — 8 thermocouples, 8 bearings, 8 inlet temperatures. It fits. It works. Just ground shields at one end. Keep fans away from the terminal block. Use the correct extension wire. And don’t buy refurbished. The CJCs are tired. The readings drift. And you won’t know until the turbine runs hot. At 2 AM. In Texas. Ask me how I know.

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