WATLOW Wattlo 998D-22KK-ARRG is a high-performance dual-channel digital controller.

Watlow 998D-22KK-ARRG is a high-performance, dual-channel digital controller from the legacy Series 998.

Specifically engineered in a vertical 1/8 DIN form factor, this model is designed to handle two independent PID control loops with a focus on specialized thermocouple high-gain inputs and solid-state relay outputs.

1. Introduction

The 996D-22KK-ARRG is a “blind” or digital-interface unit (depending on cabinet integration) that provides dual-loop thermal management.

The “22” in its configuration designates its specialized Universal Signal Conditioners, which are factory-calibrated to handle a wide variety of thermocouple types with superior stability.

This model is often utilized in industrial environments where two processes must be synchronized or controlled within a single, space-saving chassis.

2. Technical Parameter Table

3. Product Advantages and Features

Dual-Loop Efficiency: Replaces two separate 1/16 DIN controllers, reducing panel cutout needs and simplifying wiring.

Specialized High-Gain Inputs: The “22” universal signal conditioner allows for the use of rare-metal thermocouples (like R, S, and B) with high precision.

Solid State Reliability: The “KK” output configuration utilizes dual SSRs, which provide silent, wear-free switching for high-cycle PID applications.

NEMA 4X Protection: The front panel is rated to withstand washdowns and corrosive environments, making it ideal for food and chemical processing.

Isolated Circuitry: Full electrical isolation between inputs and outputs prevents ground loops and signal interference.

4. Application Cases

Cascade Control Systems: Using Channel 1 for the primary process (e.g., oil temperature) and Channel 2 for the secondary loop (e.g., heater sheath temperature).

Semiconductor Quartz Heaters: Managing internal and external heating zones in diffusion furnaces where precise thermocouple feedback is mandatory.

Plastic Injection Molding: Independent control of the nozzle and manifold temperatures in a single vertical unit.

Laboratory Furnaces: Managing high-temperature ramps using Type S or R thermocouples for metallurgical testing.

5. Other Models in the Same Series

998D-11CC-CCRG: Standard thermocouple version with Switched DC outputs.

999D: The horizontal version of the same dual-channel architecture.

Series 988: A single-channel predecessor with similar 1/8 DIN dimensions.

Modern Replacement: Watlow EZ-ZONE® PM6 (1/16 DIN) or F4T (Touchscreen) for multi-loop upgrades.

6. Installation and Maintenance

Installation

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

SSR Wiring: Note that the “KK” Solid State Relays are rated for 0.5A. If your heater exceeds this current, you must use the 998D to drive a larger external SSR or DIN-A-MITE power controller.

Thermocouple Polarity: Ensure the specialized thermocouple wire matches the input type configured in the software; reversed polarity will cause the display to show decreasing temperatures as the heater warms.

Maintenance

Visual Diagnostics: Use the “CH A” and “CH B” indicators to verify which loop is currently being adjusted.

Zero/Span Calibration: For high-accuracy applications, use the calibration menu to offset any sensor error or line resistance in long thermocouple runs.

SSR Protection: Ensure the RC suppression is checked if using inductive loads to prevent premature failure of the internal solid-state components.

7. Unique Product Description

“The Watlow 998D-22KK-ARRG is the precision vertical powerhouse of the 990-series family.

By pairing universal high-gain signal conditioners with wear-free solid-state switching, it delivers a level of dual-channel reliability that is unmatched in high-temperature environments.

It is the definitive choice for engineers who need to monitor two worlds and control them with a single, rugged interface.”