Gemo AR2-A-24VDC-8D-RTC – Compact 24 VDC Smart Relay with 8 Inputs, 5 Relay Outputs and Real-Time Clock

Designed for small control panels and straightforward machine logic, the Gemo AR2-A-24VDC-8D-RTC combines 8 digital inputs, 5 relay outputs and a battery-backed real-time clock in a compact programmable controller. A dedicated PTC temperature-sensor input is also available for applications where temperature must be included in the control sequence.

This model is intended for applications such as timed machine operation, pump and fan sequencing, lighting control, simple interlocking and other compact automation tasks. Gemo AR2 products have been available through our website since 2011.

A compact I/O configuration for simple automation

The controller operates from a nominal 24 VDC supply and provides 8 DC digital inputs. Standard input filtering is at least 8 ms, helping prevent short electrical disturbances from being interpreted as valid input changes.

Its 5 relay outputs are rated up to 250 VAC / 2 A for resistive loads. This makes the controller suitable for conventional panel circuits using contactors, signalling devices and similar loads, provided the relay ratings are respected. Inductive loads should be fitted with appropriate suppression or interface protection.

No general-purpose analog I/O is fitted to this version. The dedicated PTC channel should not be confused with a standard 0–10 V analog input.

Real-time scheduling without an external timer

The RTC suffix identifies the version with a battery-backed real-time clock. Unlike ordinary ladder timers, which measure elapsed time, the RTC works with the actual clock and calendar.

This allows weekly and annual schedules to be created directly in the controller. Equipment can therefore be started, stopped or enabled according to specific days and times without adding a separate weekly timer to the panel.

Ladder programming

Programming is carried out with GEMO Ladder Editor. The available ladder area consists of 256 program lines, 5 contact columns and 1 output column, with rising-edge and falling-edge functions available for contacts.

Program transfer is performed through the controller's RS-232 programming interface. Suitable PLC programming equipment should be used when commissioning or modifying the application.

Internal functions include 32 timers, 32 16-bit up/down counters and 32 offset counter comparators. Fast-counter functions are also available for applications where pulses must be counted faster than standard digital events.

Typical ladder scan time is around 10 ms or less, depending on the application program. Fast-counter input ON and OFF times are approximately 1.25 ms.

Where this model should not be used

The AR2-A-24VDC-8D-RTC uses relay outputs and therefore does not provide high-speed pulse / direction outputs for positioning servo or step motor systems. Motion applications requiring pulse-train positioning need a PLC or motion controller designed for that purpose.

A built-in PID control algorithm is also not provided. Closed-loop temperature, pressure or flow control should therefore be handled by a suitable process controller or a PLC with PID capability.

Local display instead of an external HMI

A 2 × 16 character backlit LCD and three programmable front-panel function keys are built into the controller. Status information, timer values, counter values, RTC information and operator messages can therefore be displayed locally.

The AR2-A-8D family is not intended for the external Modbus gateway / HMI arrangement used with larger AR2 models. If an external operator panel or Modbus RTU connection is required, a higher-level AR2 version or another PLC / HMI platform should be selected.

Fixed I/O – not expandable

Unlike the larger AR2 controllers, the AR2-A-24VDC-8D-RTC is not expandable. Its application should therefore be designed around the available 8 inputs and 5 outputs. If additional I/O is likely to be required later, an expandable AR2 model is the better choice.

Installation conditions

The controller is intended for operation between approximately 0 and 50 °C and carries an IP20 protection rating. Relative humidity should remain within the manufacturer's specified limits and condensation must be avoided.

When installed in a panel containing AC motor drives, frequency inverters, contactors or other electrically noisy equipment, control wiring should be kept away from power and motor cables wherever practical. Correct grounding and cable routing are important for reliable operation.

Programming software and documentation

The latest available GEMO Ladder Editor V2.4 programming package can be used for AR2 configuration and ladder programming.

For ladder instructions, timers, counters, RTC functions and controller settings, refer to the Gemo AR2 PLC English user manual.

Other models and commercial information are available from the Gemo price list, the Gemo Electronic main page and our PLC product group.

For model selection or technical questions, visit the Gemo contact page or contact us at gemo@otomasyonavm.com.

Installation notice: Wiring, commissioning and servicing should be carried out only by qualified technical personnel. Disconnect all power sources before working on the controller or panel, and follow the manufacturer's installation instructions and the applicable electrical-safety requirements.