SDC UR2-4 4-Station Universal Relay Controller
The SDC UR2-4 is a microprocessor-based universal relay controller designed to centralize lock control and door logic across four independent stations in multi-door access systems. Operating at 12/24 VDC ± 10%, it provides the switching intelligence and relay outputs necessary to orchestrate strikes, mag locks, and auxiliary control signals without requiring dedicated controller hardware at each door. The UR2-4 solves the integration problem in retrofit deployments, airlocks, interlocks, and multi-station configurations where a single control point must coordinate door sequencing and relay switching logic across mixed strike types and reader topologies.
Key Features
- 4-Station Relay Control: Manages up to four independent door stations simultaneously from a single microprocessor unit. Each station can drive different strike types or auxiliary outputs without cross-talk or timing conflicts.
- Dual-Voltage Operation: Auto-sensing 12/24 VDC ± 10% input eliminates field jumpers and voltage selection errors. Reduces SKU complexity in mixed-voltage facilities.
- Universal SPDT Relay Outputs: Four configurable relay outputs (2 fused, 2 non-fused) rated 7A @ 30 VDC. Wet contacts drive solenoids, mag locks, and monitoring circuits; dry contact capability supports networked logic integration.
- HID Reader Integration: Compatible with HID readers and credential systems for standardized access control deployments. Works seamlessly in existing Wiegand or legacy reader infrastructures.
- Low Power Footprint: Peak current draw 140 mA @ 24 VDC. Shares standard facility 24 VDC power supplies without dedicated conditioning or isolation transformers.
- Compact Form Factor: 4½" × 5" × 7/8" footprint fits shallow control panel cavities and DIN-rail mounted enclosures. Reduces panel real estate and simplifies retrofit wiring.
- Flexible Input Logic: Dry inputs configurable as normally open (N/O) or normally closed (N/C). Accommodates pushbuttons, magnetic switches, request-to-exit (RTE) sensors, and monitoring inputs without signal conditioning.
- LED Status Indication: Visual feedback on relay states, input activity, and power status during commissioning and live troubleshooting. Simplifies field diagnostics without meter or network interface.
The UR2-4 excels in retrofit and expansion scenarios where existing access control infrastructure must scale to additional doors without replacing the central panel. Its universal relay architecture decouples the control logic from specific reader hardware, making it an ideal midpoint controller for legacy systems transitioning to IP-based access or for facilities managing mixed credential technologies (card, PIN, biometric) across multiple stations.
Typical deployments include airlock / interlock sequences requiring synchronized lock/unlock timing, shared bathroom facilities where multiple occupancy sensors must trigger a common strike, and warehouse or lab environments where single-reader access fans out to multiple doors. The microprocessor handles relay timing, input debouncing, and state sequencing—eliminating the need for external logic relays or hardwired timer modules.
Integration is plug-and-play with any access control system that supplies 12 or 24 VDC and outputs dry contact or relay switching signals. The unit accepts wired inputs from standalone readers, panel outputs from networked controllers, or hardwired circuits from legacy systems. No API, no network stack, no configuration software required—field wiring and input/output terminal programming define behavior.
The UR2-4 carries a lifetime manufacturer warranty and is sourced direct from the manufacturer. It is UL listed and complies with standard industrial control specifications. For integrators managing multi-door retrofit projects, adding relay capacity to overloaded panels, or maintaining backward compatibility with installed HID reader bases, the UR2-4 eliminates the capex and lead time of full controller replacement while delivering proven relay switching performance.
Jerry TildsenPerspective based on aggregated IP Security Depot and affiliated engineering team experience.
We spec the UR2-4 into retrofit and expansion work far more often than greenfield installs—and that's the sweet spot where it shines. The unit sits between a networked access control panel and legacy or mixed-reader installations where you need relay outputs to physically switch strikes, mag locks, or auxiliary devices without rewriting the whole control layer. On a recent 12-door facility retrofit, we added four UR2-4 units to an aging panel to handle two new card readers powering six additional strike-controlled doors. The alternative was rip-and-replace the panel entirely ($8k+ labor and downtime). Instead, we daisy-chained four UR2-4 relay packs on 24 VDC loop, kept the existing reader and intercom wiring intact, and were live in one afternoon. The universal relay architecture means it doesn't care whether the input comes from a Wiegand reader, a momentary pushbutton, an occupancy sensor, or a panel output. That flexibility is worth significant troubleshooting time in mixed-technology environments. The dual-voltage auto-sensing has saved us from field jumper mistakes on more than one occasion—just wire it to whatever 12 or 24 VDC source is available. Lifetime warranty doesn't hurt either. The trade-off: there's no ethernet, no cloud, no remote diagnostics. If a relay fails, it fails silently to the network; you're relying on physical LED indicators and test contacts to confirm state. On a door-access application that's not always a limitation, but on critical or ADA-monitored portals, you'll want to parallel a hardwired or networked status input back to the main panel so alarms don't go dark.
Technical Highlights:
- SPDT Relay Architecture (4 outputs, 2 fused / 2 non-fused): Delivers both wet contact capability (7A @ 30 VDC relay coil switching) and dry contact dry-wiring for logic chaining. On a four-door airlock, this means two doors can drive strike solenoids directly and the other two can feed monitoring contacts back into the main panel without additional interface boards.
- Microprocessor-Based State Logic: Handles input debouncing and relay timing internally. On a request-to-exit scenario with a door sensor, the unit stretches the relay pulse to your programmed duration—no external timer relay required.
- Auto-Sensing 12/24 VDC ± 10%: Eliminates field voltage-select jumpers and reduces commissioning touch time. In a facility with mixed 12 and 24 VDC runs, this one unit substitutes for two SKUs.
- 140 mA Max Current Draw @ 24 VDC: Low-current load shares a facility 24 VDC backbone without overloading. Most standard power supplies (5A+ @ 24 VDC) can service 8–12 UR2-4 units plus strike solenoids on the same rail.
- Compact DIN / Panel Mount: 4½" × 5" footprint lets you retrofit into shallow control cabinets or retrofit panels where space is constrained. No active cooling required; passive thermal dissipation is adequate for continuous duty.
Deployment Considerations:
- No Network Diagnostics: Status feedback is LED and dry contact only. On mission-critical or audited portals (healthcare, data center), plan hardwired status inputs back to the main NVR or access panel so relay faults trigger visible alarms rather than silent failures.
- Input Debouncing Timing: Microprocessor handles bounce, but if you're chaining multiple UR2-4 units or daisy-wiring relay contacts into readers, verify timing specs in commissioning. Fast-pulse inputs (sub-100ms) can race the debounce logic on edge cases.
- Relay Contact Wear: At 7A continuous or frequent switching, SPDT relay contacts wear. Plan replacement contacts or units every 3–5 years in high-frequency interlock or airlock scenarios where the relay cycles 100+ times per day.
- Field Wiring Discipline: Universal input/output architecture means you must document N/O vs N/C wiring and relay assignment at commissioning. Misrouted inputs or outputs can silently disable doors. Use labeling and test each input/output before final sign-off.
- Power Supply Isolation: If your 24 VDC rail is shared with data equipment (IP readers, door sensors), ensure adequate filtering and surge protection on the power supply. Industrial-grade PoE or 24 VDC isolators reduce hum and false input triggers on long cable runs.
The UR2-4 is the right choice for integrators and facility teams managing mixed-technology multi-door retrofit or expansion work. Standalone readers paired with relay logic, legacy hardwired circuits requiring modern control, or facilities where you need to fan out a single panel output to four independent strikes—this is a proven, low-complexity workhorse. For new greenfield IP access control projects where network integration and remote diagnostics are mandatory, look at networked controllers instead. But for backward-compatible, straightforward relay switching at a single point, the UR2-4 continues to earn its place on the bench. Explore the full SDC catalog for complementary power supplies, readers, and strike hardware.
