Omron CJ1W-DA08C 8-Channel Analog Output Unit for CJ Series PLCs

The Omron CJ1W-DA08C is an analog output module belonging to the CJ1W series of I/O units for Omron CJ1, CJ2, and CJ2M programmable logic controllers. This unit provides eight independent analog output channels, each supporting a 4-20 mA current output. The module is used to convert digital setpoints from the PLC into continuous analog signals for controlling process actuators such as proportional valves, variable frequency drives (VFDs), chart recorders, and analog meters. Its compact design allows high-density mounting in CJ series racks.

Technical Specifications

Functional Description

The CJ1W-DA08C receives digital data from the CPU unit via the CJ-series backplane. Each channel independently converts the 8-bit digital value (0–255) into a proportional 4-20 mA current. For example, a digital value of 0 corresponds to 4 mA, and 255 corresponds to 20 mA, though scaling can be adjusted in the PLC user program. The module performs conversion at a rate of 2.5 ms per channel, with the total conversion time for all eight channels being 20 ms when all channels are active. The output current is sourced from the module's internal power supply, requiring no external loop power (but the module itself must be powered by 24 V DC).

Signal Range and Resolution

At 8-bit resolution, the 4-20 mA range is divided into 256 steps, giving an effective resolution of 0.0625 mA per step. This is sufficient for many process control applications, particularly where fine granularity is not required. For applications demanding higher resolution (e.g., precision servo valve control), the 12-bit CJ1W-DA041 or CJ1W-DA08V (voltage output) models are available. The 4-20 mA range is selected because current loops are less susceptible to voltage drop over long cable runs and are inherently immune to electrical noise.

Output Protection and Diagnostics

The CJ1W-DA08C includes protection against short circuits and overcurrent on the output channels. If a channel is shorted to ground or to another output, the module limits the current to prevent damage. The unit also performs self-diagnostics at power-up, checking internal circuitry for faults. If an error is detected, the module reports it to the CPU, which can generate an alarm. Additionally, the CJ1W-DA08C supports a hold function that allows the user to freeze the analog outputs at their current values when the PLC enters PROGRAM mode, preventing sudden changes during maintenance or troubleshooting.

Wiring and Installation

The module mounts in any CJ-series slot and connects to the backplane via a 32-pin connector. Field wiring is terminated on a removable 18-point screw terminal block (included) that accepts wire sizes from 0.2 to 2.5 mm² (24–14 AWG). Each output channel has two terminals: one for the output (OUT) and one for the common return (COM). The COM terminals are internally connected together, allowing a single wire to be used for the return path. For optimal accuracy, the load resistance should not exceed 350 Ω. Shielded twisted-pair cable is recommended for analog signal wiring, with the shield connected to ground at the module end only.

Programming and Configuration

Configuration of the CJ1W-DA08C is performed through the PLC's I/O table. The module occupies 1 word in the CIO area for output data, plus 1 word for control/status information. The user's ladder program writes 8-bit values to the corresponding CIO addresses, typically using MOV instructions. The module also supports scaling functions in the PLC to convert engineering units (e.g., 0–100%) to the 0–255 digital range. For more complex setups, function blocks are available in CX-Programmer.

Applications

The CJ1W-DA08C is used to control proportional pressure control valves, variable frequency drive speed references, analog chart recorder inputs, and pneumatic positioners. It is found in packaging machinery, conveyor systems, water treatment chemical dosing, and HVAC control panels. Its compact width (31 mm) allows multiple modules to be stacked in a single rack for high-channel-count applications.

Conclusion

The Omron CJ1W-DA08C provides a reliable, cost-effective solution for adding eight 4-20 mA analog outputs to CJ-series PLC systems, with built-in protection and simple wiring for industrial control applications.