Allen-Bradley 1769-OF4 Compact I/O 4-Channel Analog Output

Four voltage or current outputs for CompactLogix systems

The Allen-Bradley 1769-OF4 provides four single-ended analog outputs for valve positioners, variable frequency drive references and recorders. Each channel is set separately to a voltage range of ±10 V, 0-10 V, 0-5 V or 1-5 V, or to 0-20 mA or 4-20 mA, so one module can drive a mix of actuators and instruments.

Resolution is 15 bits plus sign, with accuracy of 0.5 percent of full scale at 25 °C and a repeatability of ±0.05 percent. All four channels convert in 2.5 ms with interrupts disabled or 3.8 ms with interrupts enabled, and the step response to 63 percent takes 2.9 ms. The module does not need field calibration.

Technical specifications

Loads and protection

Current outputs can drive up to 600 ohms including the wire resistance, and voltage outputs expect a load of 1 kilohm or more. Inductive loads on current outputs are limited to 0.1 mH, and capacitive loads on voltage outputs to 1.0 microfarad. Open and short-circuit protection is built in, with short-circuit current limited to 40 mA and overvoltage protection on the outputs.

At power-up and power-down the outputs may show a spike of 2.5 to -1.0 V DC for less than 15 ms, so keep actuators that must not move on a separate permissive. The module draws 120 mA at 5.1 V DC and 170 mA at 24 V DC from the backplane, a high 24 V demand that matters when a rack has several analog outputs.

Related 1769 analog outputs

The 1769-OF8C in the same document gives eight 4-20 mA outputs for loop-powered devices, and the 1769-OF4CI and 1769-OF4VI give individually isolated outputs. Choose the OF4 when you need both voltage and current output types on one module.

Selection checks before specifying the 1769-OF4

Start with a channel list that records, for every output, the receiving device, the signal type it expects and the loop resistance of the cable run. Because each of the four channels is configured on its own, a single module can feed a 4-20 mA valve positioner on one channel and a 0-10 V drive speed reference on another, but the list must show that every current loop stays inside the 600 ohm limit and every voltage input presents at least 1 kilohm. Long cable runs to remote valves in a process plant are where the current loop budget is usually spent, so measure or calculate the wire resistance rather than assuming it.

Next, add the 120 mA at 5.1 V DC and 170 mA at 24 V DC from the specification table to the existing rack budget and confirm the chosen 1769 power supply can carry the total, keeping the module within the stated power supply distance rating of 8 modules. If the actuator must stay still during the brief power-up spike described above, plan the separate permissive or interlock at the design stage rather than after start-up.

Installation in the panel

The module mounts on DIN rail or directly on the panel and occupies one slot in the Compact I/O bank. Use the wire sizes listed in the table, tighten terminal screws to the stated torque and keep analog output cables away from motor leads and contactor wiring. Shielded twisted-pair cable with the shield grounded at one end only is the usual practice for analog signals and helps keep the output steady at the far end. Label each channel at the terminal block and at the field device so later fault finding is straightforward.

Commissioning the outputs

After the module is added to the controller project and each channel range is set, force each output to a few known values and check the reading at the field device with a calibrated meter. Confirm direction of travel on valves and that a drive reference produces the expected speed change. Set and test the fault and program-mode output states for every channel so that a controller fault leaves each actuator in a safe position. Record the as-left values in the loop check sheets.

Operating environment in Oman and the GCC

The 1769-OF4 is an open-style module rated for 0 to 60 °C operation and 5 to 95 percent non-condensing humidity, so it belongs inside a suitable enclosure. In Gulf summers a panel standing in the sun can run well above the outdoor air temperature, so check the internal cabinet temperature with the 2.86 W dissipation of this module and the rest of the rack included, and add shading, filtered ventilation or air conditioning where needed. Fine dust is a common problem at desert and coastal sites; keep enclosure gaskets in good condition and filters clean. In humid coastal locations, condensation can form when an air-conditioned panel is opened, so let the cabinet equalise before opening it where possible.

Maintenance

The module does not need field calibration, so routine work focuses on the installation: periodic checks of terminal tightness, cable condition, shield connections and enclosure cleanliness, plus a comparison of commanded and measured values on critical loops during planned shutdowns. Keep the replacement terminal block, door and label part numbers from the table on the spares list.

Documents and quotation

The Rockwell Automation 1769 Compact I/O specifications document is attached. See our PLC and I/O cards catalogue, including the 1734-IB8 POINT I/O input module for distributed I/O. Confirm the exact catalog number, series letter and firmware or hardware revision on the product label, and the compatibility with your existing system, before ordering. Stock and lead time are confirmed at quotation.