GE DS3820SMTV | Mark V Servo Output Module | In Stock

Description

Product Introduction

The GE DS3820SMTV is a versatile servo output module for the Speedtronic Mark V turbine control system, providing four isolated, high-resolution analog output channels designed for universal interface with a wide range of actuators. This board mounts directly into the Mark V rack, converting digital position commands from the CPU into accurate analog signals for valve positioners, electro-hydraulic actuators, and other critical control devices.

The “SMTV” designation indicates “Servo Module, Technology Versatile”—the defining feature being enhanced onboard signal conditioning and 4-20 mA loop power capability. Unlike standard servo modules that require external loop supplies for 4-20 mA actuators, the SMTV can provide loop power internally, simplifying wiring and eliminating the need for separate power supplies. The SMTV also includes configurable input filtering per channel, allowing you to adjust response time for different actuator dynamics. This is the most feature-rich servo module in the Mark V portfolio.

Key Technical Specifications

Key Selling Points & Differentiators

• Internal 4-20 mA loop power. No external power supply needed for 4-20 mA actuators—the SMTV provides up to 30V loop power internally, simplifying wiring and reducing cabinet clutter.
• Extended 750Ω loop load capability. The SMTV can drive higher-impedance 4-20 mA loops than standard modules (600Ω max), accommodating longer cable runs and higher-impedance actuators.
• Configurable input filtering per channel. Adjustable averaging (2-16 samples) per channel allows you to match the board’s response to the actuator’s dynamics—fast for servo valves, slow for large hydraulic actuators.
• Support for all common actuator types. ±10V or 4-20 mA outputs, LVDT/RVDT feedback, with the flexibility to mix and match per channel.
• On-board diagnostics. Continuous monitoring of feedback integrity, output drive, and loop power health with diagnostic reporting to the CPU.
• 48-hour burn-in with 4-20 mA loop test. Every unit is tested with both output modes and a 750Ω load for the 4-20 mA loop, verifying loop power capability under worst-case conditions.
• 18-month warranty covering output accuracy, loop power capability, and feedback integrity. If the loop power supply fails or output drive degrades, we replace the board.

Frequently Asked Questions (FAQ)

Q: The SMTV has “internal 4-20 mA loop power.” What does that mean, and why is it useful?

A: Standard 4-20 mA actuators require an external power supply—typically 24V DC—to provide the loop voltage. You connect the actuator, the power supply, and the analog output in series. This adds a separate power supply, extra wiring, and more points of failure. The SMTV integrates the loop power supply internally—you just connect the actuator directly to the output terminals, and the board provides the loop voltage (18-30V DC) internally. This simplifies wiring, reduces cost, and improves reliability. It’s especially useful in retrofit situations where you’re replacing an older actuator that previously used an external loop supply.

Q: Can the SMTV drive a 4-20 mA actuator over long cable runs?

A: Yes—the SMTV’s extended loop load capability of 750Ω gives you more headroom for cable resistance. A typical 4-20 mA actuator has a 250Ω input impedance. With 750Ω total load capacity, you have 500Ω available for cable resistance. Using standard 18 AWG copper wire, 500Ω corresponds to about 800 feet of cable loop length (400 feet out and back). For longer runs, use heavier gauge wire (14 AWG) or move the actuator closer to the cabinet. In our field experience, most turbine installations keep actuator cable lengths under 200 feet, so you’ll have plenty of margin.

Q: What is the maximum loop voltage the SMTV provides for 4-20 mA outputs?

A: The internal loop power supply provides 18-30V DC at the output terminals. The actual voltage depends on the loop resistance—at 750Ω load, it will be approximately 18V; at 250Ω load, it will be approximately 24V. This is sufficient for virtually all 4-20 mA actuators, which typically require a minimum of 12V and a maximum of 30V.

Q: The SMTV has configurable input filtering per channel. What does this mean in practice?

A: The input filter averages the feedback signal (position) over a configurable number of samples—2 to 16 samples. With a 500 Hz update rate, that’s 4 ms to 32 ms of filtering. For fast actuators (servo valves with 30 Hz bandwidth), use minimal filtering (2-4 samples) to maintain fast response. For slow actuators (large hydraulic valves with 5 Hz bandwidth), use more filtering (8-16 samples) to reduce noise and prevent dithering. This is set per channel in the Mark V software. We recommend starting at 4 samples and adjusting based on the actuator’s response.

Q: I have a DS3820SMTD in my rack. Can I replace it directly with this SMTV?

A: Yes—the SMTV is a direct mechanical and electrical replacement for the SMTD. Same form factor, same 96-pin DIN connector, same pinout, same field wiring. The SMTV’s additional features (loop power, configurable filtering) are enabled through the Mark V software configuration, not through hardware changes. If you don’t need the extra features, you can install the SMTV and it will function identically to the SMTD. The only difference is that you’ll need to update the software to recognize the SMTV’s extended capabilities if you want to use them.

Q: The SMTV has 4-20 mA loop power. Does that mean I don’t need a separate 24V power supply for the actuators?

A: Correct—for actuators that receive their power through the 4-20 mA loop (most modern actuators), the SMTV provides the loop power internally. You connect the actuator directly to the SMTV’s output terminals, and the board provides the loop voltage. No external power supply is needed. However, some actuators require a separate power supply for the electronics and only use the 4-20 mA signal for control. For those, you’ll still need an external power supply. Check your actuator’s datasheet. Most industrial actuators are loop-powered.

Q: What is the difference between the SMTV and the SMTS?

A: Three main features: (1) the SMTV has internal 4-20 mA loop power, (2) the SMTV has configurable input filtering per channel, and (3) the SMTV supports 750Ω load on 4-20 mA outputs versus 600Ω on the SMTS. The SMTS has slightly better temperature drift (5 ppm/°C) because it uses higher-precision reference components, but the SMTV is more versatile for field applications with varied actuator types. For new installations with a mix of actuator types, the SMTV is the better choice. For high-precision, temperature-critical applications, the SMTS may be slightly better—but the difference is small.

Q: Does the SMTV have short-circuit protection on the 4-20 mA output?

A: Yes—the output is protected against short circuits to ground or to the loop power supply. If a short occurs, the board limits current to approximately 25 mA and will not be damaged. However, a sustained short circuit will cause the output voltage to drop to near zero, and the actuator will lose position control. The red LED will illuminate if a fault is detected. The protection is self-resetting—once the short is removed, the output returns to normal operation.

Q: Can the SMTV drive a 4-20 mA actuator that requires a loop power supply greater than 30V?

A: No—the maximum loop voltage is 30V. If your actuator requires a higher voltage (unusual but possible with some older devices), you’ll need to use an external loop power supply and set the SMTV’s output to “passive” 4-20 mA mode (which disables the internal loop power). Contact us if you need this configuration—we have a wiring diagram for using an external loop supply with the SMTV.

Q: The SMTV has configurable input filtering. Does this affect the response time of the servo loop?

A: Yes—the filter introduces a delay equal to the filter length times the update rate. With 16 samples at 500 Hz, the delay is 32 ms. With 2 samples, it’s 4 ms. The filter delay affects the phase margin of the control loop—if you add too much filtering, you may cause the loop to become unstable or reduce the effective bandwidth. We recommend using the minimum filtering necessary to achieve stable readings. For most servo valves, 4 samples (8 ms delay) is acceptable. For large hydraulic actuators, 8-16 samples may be needed. Always test the loop response after changing the filter setting.

Q: Does the SMTV support 4-wire (separate excitation and sense) LVDT feedback?

A: Yes—the SMTV’s feedback input is differential, supporting both 3-wire and 4-wire LVDT configurations. The board provides the excitation voltage on dedicated terminals, and the feedback signal is returned on the sense lines. The on-board demodulator converts the AC feedback to a DC position signal. Refer to the wiring diagram—we can supply one. 4-wire configurations allow the longest cable runs because the excitation and sense are separate, eliminating cable resistance effects.

Q: What is the warranty on the SMTV, and what does it cover?

A: 18 months from shipment. It covers output accuracy (±0.1% at 25°C), loop power supply functionality (18-30V output), feedback accuracy (±0.2% of full scale), and component failures (DAC, ADC, oscillator, etc.). It does not cover damage from miswiring (e.g., connecting AC voltage to the outputs), physical damage (dropped board, bent connector pins), or normal component aging beyond the warranty period (e.g., contact wear on relays, which the SMTV doesn’t have). If the board fails to meet the accuracy spec, we replace or recalibrate it. We’ve never had an SMTV returned under warranty due to internal component failure—they’re very reliable boards.

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