Line-Level Controlled Relay-5 to 50 s Delay

Ideal Use Cases

The RDL ST-ACR2 is designed for systems in which a line-level audio signal must operate a relay. It is suited to integrations that require relay activation when audio reaches a selected threshold, followed by a controlled release period after the signal drops below that threshold. Its 10 kΩ balanced bridging audio input may be connected to either balanced or unbalanced sources.

The module also provides an open-collector control output rated at 25 mA. This output is suitable for driving indicators or a slave LCR relay. Double-pole, double-throw contacts support relay-controlled switching within the specified voltage, current, and power limits.

Why Choose This Model

The ST-ACR2 combines adjustable audio detection with an adjustable nominal relay release delay of 5 to 50 seconds. Its SENS potentiometer sets input sensitivity from -30 dBu to 0 dBu, while the audio-threshold LED provides a visible reference during adjustment. The DELAY control determines how long the relay takes to release after the audio drops below the selected threshold.

Activation response time is 25 ms, and the specified retrigger delay is 250 ms. These defined timing characteristics make it possible to select the detection level and release behavior required for the connected system without adding a separate audio detector and relay module.

Installation and Integration

The audio input presents a 10 kΩ balanced bridging connection and supports balanced or unbalanced wiring. During setup, apply the line-level source and adjust the SENS potentiometer while observing the threshold LED. The module can be set to trigger on signals from -30 dBu through 0 dBu. The DELAY control then sets the nominal relay release interval between 5 and 50 seconds.

Power must be ground-referenced 24 Vdc at 50 mA, based on a maximum 20 mA load at the SLAVE output. Recommended power supplies are the PS-24AS for the USA and the PS-24AX for international use; a power supply is not included. The module measures 0.7 inches high by 3 inches wide by 1.6 inches deep, equivalent to 1.7 by 7.6 by 3.9 cm. Its specified ambient operating range is 0°C to 55°C.

Performance Highlights

The ST-ACR2 uses double-pole, double-throw relay contacts. Published maximum switching ratings are 60 W or 125 VA, 220 Vdc or 250 Vac, and 2 A. The separate open-collector control output is rated at 25 mA and can operate an indicator or slave LCR relay. An audio-threshold LED supports sensitivity adjustment, while the 25 ms activation response, 250 ms retrigger delay, and adjustable 5-to-50-second nominal release delay define the module’s timing performance.

The balanced bridging input accepts line-level audio and can also be wired unbalanced. Together, the input configuration, adjustable threshold, visual threshold indication, relay contacts, and control output provide the core functions needed for audio-controlled relay operation.

What Makes It Different

This model places audio sensing, threshold adjustment, delayed relay release, DPDT switching contacts, and a slave control output in one compact module. The adjustable sensitivity range allows the trigger point to be matched to signals between -30 dBu and 0 dBu. Unlike a fixed release arrangement, its DELAY control permits a nominal release setting anywhere from 5 to 50 seconds.

The threshold LED is particularly useful during configuration because it directly indicates when the selected audio threshold has been reached. Balanced or unbalanced input compatibility also gives the installer flexibility when connecting the module to an existing line-level signal path.

Final Assessment

The RDL ST-ACR2 is a focused solution for converting the presence of line-level audio into relay and open-collector control outputs. Its adjustable sensitivity, visible threshold indication, 25 ms activation response, DPDT contacts, and adjustable 5-to-50-second nominal release delay provide clearly defined control over audio-triggered switching. For systems operating within its stated contact, power, and environmental ratings, it offers a compact, configurable integration option.