Video Controlled Relay-BNC

The RDL TX-VCR is a video-controlled relay that detects the presence or loss of an NTSC or PAL video signal. It accepts a ground-referenced BNC input from 0.5 V p-p to 1 V p-p and provides a BNC loop output for insertion into a terminated video line. Its single-pole, double-throw relay supplies normally open or normally closed dry-contact outputs, while the front-panel SYNC LED indicates when valid video is detected.

Ideal Use Cases

The TX-VCR is suited to systems that require a dry-contact response based on whether a valid video signal is present. It can be used where video presence must be detected, where signal loss must be identified, or where another device needs to receive a normally open or normally closed contact state from a video source. Detection of both NTSC and PAL signals allows the relay to serve either format without requiring separate models.

Its loop-through arrangement supports installations in which the monitored signal must continue to a downstream 75 Ω load. The unit can also operate at the end of a video line when its supplied 75 Ω terminator is installed on the LOOP OUT connector.

Why Choose This Model

The TX-VCR combines signal detection, visual status indication, and relay control in a compact unit measuring 1.4 inches high, 3.0 inches long, and 1.2 inches wide. The detection circuit bridges a 1 V video line, allowing the device to monitor the signal while the loop output feeds a properly terminated load.

The SPDT relay provides both N/O and N/C contact options. This gives the installer a choice of contact behavior without requiring a different relay model. The specified maximum switching power is 60 W, with ratings listed as 220 Vdc, 125 Vac, and 2 A.

Installation and Integration

Video connects through ground-referenced BNC jacks. The input accepts video levels from 0.5 V p-p through 1 V p-p. For loop-through operation, connect the incoming source to INPUT and route LOOP OUT to a connected load terminated at 75 Ω. The LOOP OUT must be terminated either by the connected 75 Ω load or by the supplied 75 Ω terminator.

If the TX-VCR is positioned at the end of the line, install the supplied terminator on LOOP OUT. This supports terminated operation while retaining the unit’s video-detection function. The dry-contact control connection can use either the normally open or normally closed relay contact according to the required control arrangement.

Power may be supplied from a ground-referenced 12 to 33 Vdc source or a 12 to 24 Vac source. Current requirement is 75 mA. The recommended power supplies are the PS-24AS for the USA and the PS-24AX for international use; neither is included.

Performance Highlights

• Detects the presence of valid NTSC or PAL video.
• Detects loss of the monitored video signal.
• Accepts 0.5 V p-p to 1 V p-p video through a ground-referenced BNC input.
• Provides a ground-referenced BNC LOOP OUT connection.
• Supports bridging or terminated operation.
• Provides single-pole, double-throw N/O or N/C dry relay contacts.
• SYNC LED illuminates while valid video is being detected.
• Operates from either AC or DC power within the specified ranges.
• Supports ambient operating temperatures from 0° C to 55° C.

What Makes It Different

Rather than providing only a visual indication of signal state, the TX-VCR converts video detection into an accessible relay-contact output. The combination of BNC loop-through connectivity and SPDT dry contacts allows the video path and control path to be integrated through one device. Its ability to bridge a 1 V video line or terminate the end of the line provides two documented installation configurations.

The broad power-input range also provides flexibility when integrating the unit with available ground-referenced AC or DC supplies. Valid-video status remains directly visible through the SYNC LED during operation.

Final Assessment

The RDL TX-VCR provides a focused solution for detecting NTSC or PAL video presence and loss while producing an SPDT dry-contact output. Its BNC input and loop output, supplied 75 Ω terminator, selectable N/O or N/C contacts, AC or DC power compatibility, and visible SYNC indication make its signal path and control behavior straightforward to integrate. The result is a compact video-monitoring relay with clearly defined termination, power, contact, and operating requirements.