DS3800NPOC | 0–10 V / 4–20 mA Output – High Current

Description

Product Introduction

The fuel valve on a 150 MW turbine doesn’t care about your 250 Ω load spec—it’s got a coil resistance of 400 Ω and it needs 20 mA to crack open. The standard NPDA tops out at 250 Ω and can’t drive it. The DS3800NPOC is the board that GE built for exactly these high-impedance actuators, with output drivers that can handle up to 750 Ω in current mode and 20 mA in voltage mode—double the drive capacity of the NPDA.

This board is the heavy lifter in the Mark VI analog output lineup. It shares the same eight-channel, 16-bit architecture as the NPDA, but the output driver stage is entirely different: larger transistors, beefier heatsinks, and a higher-voltage rail that gives it the muscle to drive high-impedance loads. The board supports 4–20 mA current loops (with an external 24 V loop power supply) and 0–10 V voltage outputs, configurable per channel with onboard jumpers—though in my experience, 95% of applications use the current output for large fuel valves. The DACs are updated simultaneously every 10 ms, and the board maps its data into the VME address space at 0xE000–0xE010. Power draw is about 9 W—significantly higher than the NPDA’s 7.5 W due to the larger driver transistors. GE released this board around 2012 for heavy-duty gas turbines and large steam turbine applications.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

The NPOC is the most demanding board to test—we have to verify output accuracy across a 750 Ω load, and the thermal management is critical. A board that passes at 250 Ω can fail at 750 Ω.

Incoming Verification & Traceability
The board arrives with an OEM packing slip; we cross-reference the serial number against GE’s factory records. Genuine NPOC boards have a serial prefix starting with “NO” followed by a production week code. The UV hologram on the GE label must show a sharp eagle pattern under 365 nm light. Visual inspection: the P2 connector’s gold plating must be flawless. We inspect the output driver transistors (large TO-247 packages with individual heatsinks near the P2 connector)—they should show no discoloration and the thermal paste between the transistor and the heatsink should be intact. The heatsinks themselves should be silver—any darkening indicates thermal stress from a previous installation.

Live Functional Test (GE Mark VI Simulator with High-Load Test Rig)
We insert the board into a powered Mark VI test chassis with a CPU running firmware v5.2. Power-on self-test: green LED on within 200 ms, yellow LED flashes once for VME handshake. We connect the P2 connector to a custom test harness that includes:

• 750 Ω precision resistors for current mode (the maximum rated load)
• A Fluke 289 multimeter for current measurement
• A Fluke 115 for voltage measurement
• An IR thermometer to monitor transistor temperature

The test software writes commands to the VME memory map at 0xE000–0xE010: 0%, 25%, 50%, 75%, and 100% of full scale. We measure the output current with the Fluke 289—each output must be within ±0.15 mA at 20 mA (that’s GE’s spec for the NPOC at full load, wider than the NPDA’s 0.1 mA). We then run a step-response test: command a step from 0% to 100% and measure the settling time to 0.1%—must be under 6 ms (the NPOC is slightly slower than the NPDA due to the larger output capacitance).

High-load thermal test: We drive all eight outputs at 20 mA into 750 Ω loads and run the board for 30 minutes at 25 °C ambient. We measure the output driver transistor temperatures with the IR thermometer—each must stay below 75 °C at 25 °C ambient. Any transistor exceeding 75 °C fails (the spec derates from there).

Voltage mode test: We configure some channels to 0–10 V and connect 500 Ω loads. We command 0%, 25%, 50%, 75%, and 100% and measure the output voltage—must be within ±10 mV at 10 V.

Electrical Safety & Isolation
Insulation resistance: we apply 500 VDC between all P2 output terminals and chassis ground using a Megger MIT525—pass threshold is 10 MΩ; typical boards measure over 100 MΩ. Ground continuity from mounting holes to VME ground: below 0.05 Ω.

Firmware & Hardware Config Verification
The firmware EPROM at U12 must show a label with “NPOC-FW-1.1” and a GE logo. We photograph the S1 DIP switches for VME address and the jumper banks (W1–W8) for output type per channel. Factory default for this part number is all outputs set to 4–20 mA with base address 0xE000.

Final QC & Packaging
A 2-hour burn-in at +55 °C with all eight outputs driven to 50% (12 mA, 5 V) into 750 Ω loads follows the functional test. Any output drifting more than 0.1% of full scale fails. We then re-check transistor temperatures—must stay below 85 °C at 55 °C ambient. The board goes into a fresh ESD bag with a desiccant pack, sealed, and packed in a double-walled carton with 2-inch foam padding. The QC label includes test engineer initials, a test ID, a “Passed” stamp, and a QR code linking to the test report.

Field Replacement Pitfalls

I’ve replaced about 25 of these NPOC boards over the years—mostly on large gas turbines where the fuel valve actuators need the high drive capacity. Here’s what I’ve learned the hard way.

The 750 Ω Load—That’s the Absolute Maximum
The NPOC can drive 750 Ω, but only at 25 °C. At 55 °C ambient, the maximum load derates to 500 Ω. I saw a case in a Persian Gulf plant where the ambient was 50 °C and the actuator had a 650 Ω coil. The board drove it to 18 mA but couldn’t reach 20 mA—it was derating. The turbine couldn’t reach full load. The solution: move the board to a cooler slot or add a signal conditioner. Calculate your actuator’s coil resistance at operating temperature. The resistance of a copper coil increases with temperature—a 400 Ω coil at 25 °C is about 460 Ω at 85 °C. You might be closer to the limit than you think.

The Loop Power Requirement—It’s Higher
The NPOC’s current outputs require an external 24 V loop power supply, just like the NPDA. But because the NPOC can drive 750 Ω, the loop power supply needs to deliver enough voltage to overcome that impedance. At 20 mA and 750 Ω, the voltage drop is 15 V. Add the board’s internal drop (about 5 V), and you need at least 20 V at the board’s output terminals. If your loop power supply is only 24 V, you have only 4 V of margin. I saw a case where a plant used a 24 V supply with a 5% tolerance—23 V. At 750 Ω, the board couldn’t reach 20 mA because the supply couldn’t provide enough voltage. Measure your loop power supply voltage under load. If it’s below 22 V at 20 mA, you need a 28 V supply or a lower-impedance actuator.

The Output Transistors Run Hot—Derating Matters
The NPOC’s output driver transistors are larger than the NPDA’s, but they still run hot. At 50% duty (12 mA) into a 750 Ω load, the transistors dissipate about 1.5 W each. At 100% duty (20 mA), they dissipate about 2.5 W. That’s a lot of heat for a 6U VME board. I saw a case where a technician installed an NPOC in a rack with poor airflow—the transistors hit 95 °C at 55 °C ambient and the board thermal-shutdown. The turbine tripped on “Output Channel Fault.” Check your rack’s airflow. The NPOC needs at least 50 CFM across the board at 55 °C ambient. If your rack has less, consider moving the NPOC to a slot with better airflow or adding a fan.

The Address—0xE000 Might Conflict with Other High-Power Boards
The NPOC’s default address is 0xE000. GE assigned this address range to high-power output boards. If you have another high-power board (say, an NPOC1A or an NPDC) that also uses 0xE000, you’ll have an address conflict. I saw a case where a technician installed two NPOC boards without checking the addresses—the CPU’s writes went to both boards, and the actuator control became erratic. ❗ Read the address configuration file from the CPU before you install. Set S1 to an address that doesn’t conflict with any other board in the rack.

The Output Jumper—Don’t Forget the High-Current Mode
The NPOC has a jumper setting for “high-current mode” that’s separate from the output type jumper. If you’re driving a load above 500 Ω, you need to set the high-current jumper to enable the higher voltage rail. I saw an engineer set the output type to 4–20 mA but forgot the high-current jumper—the board operated in the standard NPDA mode and couldn’t drive the 750 Ω load. Check the jumper settings in GE document GEH-6702. The high-current jumper is W9, and it’s easy to miss.

Get these five right and you’ll cut rework time by 90%—and more importantly, you won’t be explaining to a plant manager why the new output board can’t drive the fuel valve to full open.

New Original vs. Refurbished: Why It Matters

We call this board “New Original (New Surplus)” for a reason. Let’s break down what that actually means for a part this age.

What You’re Getting From Us:
This DS3800NPOC was manufactured by GE in their Salem, Virginia facility, likely around 2012–2014. It has never been installed in a field chassis. The P2 connector’s gold plating is flawless with zero insertion marks. The output driver transistors are fresh, with no signs of thermal stress—the thermal paste is still pliable and the heatsink fins are clean. Our boards are either in the original GE sealed anti-static bag, or we’ve opened the bag solely for the functional test described above. When we open it, we replace the bag with a new ESD-safe one and seal it with a tamper-evident label. We include a photo of the board before and after testing.

The Refurbished Risk:
High-current output boards are the most abused boards in the refurbished market. The output driver transistors wear out—their gain decreases over time, especially if they’ve been run hot in a previous life. I tested a refurbished NPOC that passed the low-load test (250 Ω) but failed the high-load test (750 Ω)—the transistors couldn’t deliver 20 mA at the full load. The board had been cleaned and looked new, but the transistors were worn out. Our failure tracking shows refurbished high-current boards have a 5× higher failure rate in the first year compared to new surplus, primarily due to output derating under high load. One unplanned shutdown on a 150 MW gas turbine costs about $30,000 in lost generation and restart fuel—that’s 12 times the price difference between a refurb and a new board.

We don’t just “recondition”; we confirm provenance. Every board we sell has a photographed OEM serial number traceable to the factory. We provide a visual inspection report and the functional test results—including the 750 Ω loaded accuracy data and thermal measurements. That’s your paper trail. Our price sits about 25% above refurbished but roughly 30% below GE’s current list price for a new board (though GE hasn’t manufactured this board since 2018). The delta is the cost of us sitting on 40 boards, testing each one under full load at 750 Ω, and offering a 12-month warranty. We don’t offer a 100% guarantee—nothing in a Mark VI cabinet is guaranteed—but we will replace or refund any board that fails due to a manufacturing defect on our test.

Performance Benchmarks & Test Results

We collect performance data from every board we test. Here is a summary from a recent batch of 10 DS3800NPOC boards, tested under controlled conditions.

• Test Environment:
  • System: GE Mark VI Simulator (VME Backplane, CPU firmware v5.2)
  • Temperature: 25 °C ambient, forced air at 50 CFM
  • Power Supply: +5 VDC @ 1.8 A (measured as 5.03 VDC), ±15 VDC @ 0.4 A (measured as 15.0 VDC)
  • Load: 750 Ω precision resistors (max load)
  • Firmware Version: v1.1 (OEM factory)
• Measured Performance Data:

One board showed 0.18% error at 20 mA into 750 Ω on channel 6—above the 0.15% spec at max load. We traced it to a faulty driver transistor and rejected the board. Our threshold for passing is stricter than GE’s for some parameters: we reject any board with error above 0.12% at 750 Ω (GE allows 0.15%). The final output is a board that’s as close to factory specification as we can get without a full GE factory recalibration. It will perform identically to a board you pulled out of a sealed GE bag in 2014.

A-B 1756-L75
Fanuc/ ǿ A06B-6164-H364#H580
A-B 1756-L63
A-B 1756-L63