WATLOW 999D-11FF-AARG Dual-channel digital unit with universal process outputs

Watlow 999D-11FF-AARG is a high-performance, dual-channel digital controller from the legacy Series 999.

 Distinguished by its horizontal 1/8 DIN form factor, this model is designed for applications requiring two independent PID loops and specialized "Universal Process" analog outputs for driving complex loads.

1. Introduction

The 999D-11FF-AARG is the horizontal counterpart to the vertical 998 series. It integrates two separate PID controllers into a single unit, specifically optimized for Universal Process Outputs.

 The "FF" in the model code indicates that both Channel A and Channel B provide isolated analog signals (e.g., 4-20mA or 0-10VDC) rather than simple on/off switches.

 This makes it a preferred choice for controlling proportional valves, variable frequency drives (VFDs), or phase-angle fired SCR power controllers.

2. Technical Parameter Table

3. Product Advantages and Features

Isolated Proportional Control: Unlike standard relay outputs, the "FF" universal process outputs provide smooth, continuous analog signals, essential for fine-tuned flow or pressure control.

Horizontal Profile: Designed specifically for low-profile control panels or equipment racks where vertical height is limited.

Dual Display Visibility: Clear, high-contrast LED displays allow the operator to monitor both the actual temperature (Red) and the target setpoint (Green) simultaneously.

Enhanced PID Logic: Supports complex control strategies, including auto-tuning for each channel independently, ensuring rapid stability upon startup.

NEMA 4X / IP65: Front-panel protection ensures the unit remains operational even in environments prone to dust or occasional spray.

4. Application Cases

Proportional Valve Actuation: Using the 4-20mA output to precisely position steam valves in food sterilization or chemical processing.

VFD Speed Modulation: Controlling the speed of two separate cooling fans or pumps based on process temperature.

Multi-Zone Infrared Drying: Managing two distinct IR lamp zones using 0-10V signals to drive phase-angle SCRs for uniform drying.

Cascade Control: Implementing primary and secondary loop control (e.g., jacket vs. product temperature) in pharmaceutical reactors.

5. Other Models in the Same Series

999D-11CC-AARG: Version with Switched DC outputs for driving SSRs.

998D-11FF-AARG: The vertical version of this exact controller.

Series 989: The single-channel predecessor in a horizontal format.

Modern Replacement: Watlow F4T (with analog output modules) or EZ-ZONE PM6 for modernized 1/16 DIN horizontal upgrades.

6. Installation and Maintenance

Installation

Cutout: Requires a horizontal 1/8 DIN cutout ($92text{mm}$ wide $times 45text{mm}$ high).

Output Selection: The "Universal" F-output is configured via the software menu. Ensure the output type (e.g., 4-20mA) matches the input requirement of your external device before wiring.

Shielding: Proportional analog signals are susceptible to noise; always use twisted-pair shielded cable for the 4-20mA/0-10V output runs.

Maintenance

Output Verification: Periodically check the analog output signal with a multimeter. If the 4-20mA signal "clamps" at 20mA despite the process not being at max, check for excessive loop resistance (typically max 800$Omega$).

Menu Lockout: Utilize the software lockout feature to prevent accidental changes to the output scaling (Zero/Span), which could disrupt proportional control.

Cleanliness: Use a damp, soft cloth to clean the front overlay. Avoid solvents that can fog the LED windows or degrade the tactile buttons.

7. Unique Product Description

"The Watlow 999D-11FF-AARG is the horizontal 'brain' for proportional process control. 

By merging two independent loops with high-resolution analog outputs, it provides the smooth, step-less control required for the most delicate industrial processes.

 It is a legacy masterpiece of precision, designed to fit where others can't and perform where others won't.