Description
Product Introduction & Engineering Value
When a safety-critical 24 VDC trip solenoid sits idle for months or years, a broken field lead or shorted field coil can quietly render your Emergency Shutdown (ESD) system useless. The Triconex 3625 Supervised Digital Output (SDO) module eliminates this hidden vulnerability by bringing active loop monitoring directly to low-voltage field devices.
Using a quadruplicated output switch matrix driven by three independent TMR processor channels, the 3625 continuously injects non-disruptive micro-test pulses into each of its 16 channels. This gives control engineers real-time visibility into field wiring open circuits, field short circuits, and blown fuses—catching field faults before an emergency demand occurs, all without cycling your process valves.
Technical Specifications
- Output Channels: 16 commoned, supervised digital output points
- Nominal Output Voltage: +24 VDC
- Operational Voltage Range: +18 to +30 VDC
- Maximum Current Rating: 1.5 A per channel (up to 4.0 A surge for <10 ms)
- Minimum Required Load: 15 mA per channel (to maintain loop diagnostics)
- Off-State Leakage Current: <2.0 mA
- ON-State Voltage Drop: <1.0 VDC at full rated current
- Point-to-Point Isolation: 1500 VDC functional isolation
- Baseplate Fusing: 2.0 A fast-acting fuse per point on the external termination panel
- Logic Power Dissipation: <10 W internal logic load
Field Application & The “Trench” Experience
The Trench Story
During a turnaround at an offshore gas compression platform, control technicians ran into a nagging LOAD fault on a critical fuel gas shut-off valve loop powered by a 3625 card. The valve opened and closed manually fine during dry runs, but the card insisted on flagging an alarm. Inspection revealed that an upgraded low-power 24 VDC solenoid had been installed on the valve—drawing only 10 mA of hold-in current. Because this was below the 3625’s 15 mA diagnostic threshold, the module interpreted the low current as an open field wire. Installing a small load resistor across the termination panel restored proper diagnostic current and cleared the alarm instantly.
Specific Field Application Scenarios
- Refinery Fire & Gas Deluge Valves: Driving and continuously monitoring 24 VDC actuation solenoids on deluge fire-water systems.
- Hydrocarbon Pipeline Isolation Valves: Driving 24 VDC interposing relays for automated emergency block valves (EBVs).
- Burner Management Fuel Cut-Off Systems: Controlling main fuel trip (MFT) safety shut-off solenoids on industrial power boilers.
- 3625
- 3625
Transparency SOP: QA & Testing
- Step 1: Visual & Pin Alignment Inspection
We check backplane edge connectors for pin straightness, inspect PCB conformal coating, and verify mechanical card alignment.
- Step 2: Powered Rig Initialization
The 3625 module is installed in an active Tricon test rack to verify triple power rail health, microprocessor startup, and TriBus communications.
- Step 3: 24 VDC Full Load & Loopback Verification
Every channel is driven at +24 VDC with a 1.5 A load to measure switching response, check voltage drop (<1.0 VDC), and verify off-state leakage stays within limits.
- Step 4: Active Supervision Diagnostic Routine
We simulate open field wires, direct shorts, and blown field fuses to confirm that the onboard microprocessors accurately trigger diagnostic bits and illuminate front-panel LED indicators.
The Veteran’s Tech Trap Guide
⚠️ Mind the 15 mA Minimum Load: Like its high-voltage relative (the 3623T), the 3625 requires a minimum load current (15 mA) to verify loop continuity. Connecting high-efficiency modern solenoids or interposing relays that draw under 15 mA will trigger false “LOAD” alarms. If your load is under 15 mA, install a parallel load resistor kit directly across the field termination terminals.
PRO TIP: Solenoid Flyback Suppression Inductive kickback from 24 VDC solenoids can generate sharp voltage spikes when deactivated. Even though the 3625 has internal protective circuits, long-term exposure to unsuppressed inductive spikes will stress output transistors. Always land flyback suppression diodes or MOVs directly across the solenoid coil in the field junction box.
⚠️ Check the ETP Fuse First: If an output channel loses 24 VDC output power, do not pull the 3625 card right away. The 2.0 A fast-acting fuses are located on the External Termination Panel (ETP), not inside the module itself. Always check the ETP fuse state and verify field power supply voltage before replacing the module.
Dynamic FAQ
Q: What is the primary difference between the Triconex 3625 and the 3623T?
A: Voltage level and current capacity. The 3625 operates on +24 VDC nominal loops with up to 1.5 A per channel, while the 3623T is designed for 120 VDC nominal loops up to 0.8 A per channel. Both offer full SDO field loop supervision.
Q: Can I hot-swap a faulted 3625 card while the Tricon system is live?
A: Yes. The 3625 supports online hot-swapping. Inserting a new module into an adjacent spare slot allows the Tricon Main Processors to run background checks and synchronize TMR output state before you safely pull the faulted card.
Q: Does the 3625 require a specific External Termination Panel (ETP)?
A: Yes. The 3625 must be paired with a compatible 24 VDC SDO termination panel that routes 24 VDC field power and houses the individual 2.0 A channel fuses.
Q: What condition are your surplus 3625 cards in, and what is the warranty?
A: All units are thoroughly bench-tested, cleaned, reconditioned as needed, and shipped with a full 1-year functional replacement warranty alongside full test documentation.
Q: Why does the 3625 show a red LED when field voltage drops below 18 VDC?
A: The 3625 actively monitors field power rail health. If field voltage drops below the 18 VDC minimum operating threshold, the module logs a power diagnostic fault to prevent unreliable solenoid actuation under brownout conditions.
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