Allen-Bradley 1791-N4V2 Analog Block I/O 4 Input 2 Output

Allen-Bradley 1791-N4V2 Analog Block I/O Module with Voltage Outputs

Product Introduction

The Allen-Bradley 1791-N4V2 belongs to the 1791 Block I/O family. This analog combination module features four selectable input channels and two analog voltage output channels. You can configure all four inputs as either current inputs or voltage inputs. Therefore, this module adapts to various field sensor types.

The 1791-N4V2 provides high accuracy for demanding applications. Its absolute accuracy reaches 0.1% at 25°C. Additionally, the linearity rating is 0.05% at 25°C. These specifications make this module suitable for precision process control.

The output channels include indefinite short circuit protection. This feature protects both the module and your connected devices. Consequently, you can operate with confidence even in demanding industrial environments.

Technical Specifications of the 1791-N4V2

The 1791-N4V2 communicates with controllers through block transfer or discrete transfer methods. It works seamlessly with PLC-2, PLC-3, PLC-5, and SLC family controllers. The block throughput depends on your controller's data transfer rates.

After receiving output data from the controller, the module updates its voltage outputs. This update occurs every 10 milliseconds per output channel. Input channels update at a different rate. Specifically, each input channel updates every 108 milliseconds.

Input Specifications

• Number of inputs: 4 (selectable as current or voltage)

• Update rate per channel: 108 ms

• Absolute accuracy: 0.1% at 25°C

• Linearity: 0.05% at 25°C

• Common mode rejection: -75 dB

Output Specifications

• Number of outputs: 2

• Output type: Analog voltage

• Output impedance: Less than 1 ohm

• Output update rate: 10 ms per channel

• Short circuit protection: Indefinite

Power and Environment

• Weight: 0.57 kg (1.25 lbs)

• Compatible controllers: PLC-2, PLC-3, PLC-5, SLC families

Understanding Protection Features

The 1791-N4V2 offers indefinite short circuit protection on its output channels. This feature is particularly valuable. It means the outputs can withstand a short circuit condition for an unlimited duration. The module will not suffer damage.

Furthermore, the common mode rejection rating of -75 dB is excellent. This rating means the module rejects unwanted noise effectively. Therefore, you can use the 1791-N4V2 in electrically noisy environments. For instance, near variable frequency drives or welding equipment.

Installation Guidelines for the 1791-N4V2

First, disconnect all power before starting the installation. Then mount the 1791-N4V2 on a DIN rail or panel. Ensure the module is properly secured and level.

Next, configure your four input channels. Decide whether you need all current inputs or all voltage inputs. You cannot mix input types on the same module. After making this decision, wire your field sensors accordingly.

Then wire the two analog voltage outputs to your receiving devices. Typical connected devices include analog actuators, chart recorders, or control valves. Because the outputs have indefinite short circuit protection, you have an extra layer of safety.

Finally, connect the communication interface to your controller. Set the appropriate node address. Configure block transfer or discrete transfer in your PLC program based on your controller type.

Important Configuration Notes

The 1791-N4V2 requires all four inputs to use the same signal type. You must choose either current inputs for all four channels. Alternatively, you can choose voltage inputs for all four channels. Mixing signal types on a single module is not supported.

The input update rate is 108 ms per channel. Therefore, total input scan time depends on how many channels you use. For example, using all four inputs requires 432 ms for a complete update cycle. Plan your control loop timing accordingly.

Mechanical and Environmental Parameters

The 1791-N4V2 weighs only 0.57 kg (1.25 lbs). Its compact size fits easily into crowded control cabinets. The module handles common mode noise exceptionally well with its -75 dB rejection rating.

Packaging List

• 1 x Allen-Bradley 1791-N4V2 Analog Block I/O module

• 1 x Terminal block (factory-installed)

• 1 x Quick reference guide (printed)

• No calibration certificate included

• No warranty document included

Shipping Information

We ship all orders via FedEx, UPS, or DHL. Delivery typically takes 3–7 business days depending on your location.

Frequently Asked Questions (FAQ)

1. Can I mix current and voltage inputs on the same 1791-N4V2?
No. All four inputs must use the same signal type. You configure them as all current or all voltage. Choose based on your field devices before installation.

2. What does "indefinite short circuit protection" mean for the outputs?
It means the output channels can withstand a short circuit indefinitely. The module will not be damaged. This protection is automatic and does not require external fuses.

3. Why is the input update rate slower than the output update rate?
Inputs update at 108 ms per channel because of analog-to-digital conversion time. Outputs update faster at 10 ms per channel because they only require digital-to-analog conversion. This difference is normal for analog modules.

4. Is the 1791-N4V2 compatible with SLC 500 controllers?
Yes. The 1791-N4V2 works with SLC family controllers. Communication uses discrete transfer. You do not need complex block transfer programming for SLC systems.

5. What is the significance of the -75 dB common mode rejection?
This rating indicates excellent noise rejection. The module ignores unwanted signals common to both input terminals. Therefore, you can use the 1791-N4V2 reliably near motors, drives, and other noisy equipment.