WATLOW 998D 998A Digital/Analog Dual-Channel Base Unit

Watlow 998D is a high-performance, digital dual-channel temperature and process controller. Known for its vertical 1/8 DIN form factor,

 it is a legacy workhorse in the industrial automation sector, particularly valued in the semiconductor and heat-treating industries for its high-accuracy PID logic.

1. Introduction

The 998D Digital Dual-Channel Base Unit is designed to manage two independent process loops within a single compact chassis.

 By consolidating two controllers into one unit, it significantly reduces panel space and wiring complexity.

 This unit features dual four-digit LED displays that provide real-time feedback for both loops simultaneously.

 Although now discontinued by the manufacturer, it remains a critical component in many existing industrial systems due to its reliability and precise control.

2. Technical Parameter Table

3. Product Advantages and Features

Dual-Loop Synchronization: Capable of controlling two separate heating/cooling zones independently or in a coordinated fashion (e.g., differential control).

High Calibration Precision: Offers a calibration accuracy of 0.1%, which is essential for laboratory-grade or semiconductor applications.

Isolated Circuitry: Opto-isolated inputs and outputs prevent ground loops and electrical noise from interfering with sensitive process readings.

Vertical Space Efficiency: The vertical orientation is ideal for narrow panel layouts where horizontal width is limited.

Retransmission Ability: Can be configured to retransmit the process value or setpoint to a remote recorder or PLC.

4. Application Cases

Environmental Test Chambers: Controlling both temperature and humidity loops in a single unit.

Semiconductor Quartz Heaters: Managing the inner and outer heating elements of a wafer processing pedestal.

Industrial Kilns: Syncing multiple heat zones to ensure uniform temperature gradients during firing.

Plastic Extrusion: Independent control of the barrel and die-head temperatures in a compact dashboard.

5. Other Models in the Same Series

The 998D belongs to the larger Anafaze-legacy family of multi-loop controllers:

Series 999: The Horizontal 1/8 DIN equivalent of the 998.

Series 996: Single-channel predecessor.

Series 997: The dual-channel base unit for chassis-mount applications.

Series 988: A legacy 1/8 DIN family with similar interface logic but older hardware.

6. Installation and Maintenance

Installation

Cutout: Prepare a vertical 1/8 DIN opening ($45text{mm} times 92text{mm}$).

Wiring: Use shielded twisted-pair wire for all sensor inputs. Ensure AC power lines are routed away from low-voltage signal cables.

Grounding: Connect the controller's ground terminal to a solid industrial earth ground to ensure display stability and communication reliability.

Maintenance

Memory Check: The 998D stores parameters in non-volatile memory. If the unit loses setpoints after a power cycle, the internal battery or capacitor may require servicing.

Cleaning: Use a damp, soft cloth to clean the front membrane keypad. Avoid harsh solvents that can cloud the LED windows.

Recalibration: Annual verification of the A/D converter is recommended using a certified process calibrator to maintain the 0.1% accuracy standard.

7. Unique Product Description

"The Watlow 998D is the vertical sentinel of the industrial panel. 

It masters the art of dual-channel control, allowing two separate processes to be viewed and adjusted from a single high-contrast interface. 

It is a legacy masterpiece of efficiency, providing laboratory-grade PID precision in a rugged, space-saving format that has defined reliability for a generation of thermal engineers.