WATLOW 996D Single-Channel Digital Temperature/Process Controller

Watlow 996D is a precision single-channel digital temperature and process controller.

It served as the immediate predecessor to the dual-channel 997 series and was engineered for the stringent accuracy requirements of the semiconductor and high-tech manufacturing industries.

1. Introduction

The 996D is a compact, high-performance controller designed to manage a single thermal or process loop. It features a bright digital display and a tactile keypad for local configuration.

While now discontinued, it remains a staple in legacy semiconductor tools (such as wafer tracks and diffusion furnaces) due to its high sampling rate and specialized OEM firmware options.

It is often found in chassis-mount or 1/8 DIN configurations within complex industrial cabinets.

2. Technical Parameter Table

3. Product Advantages and Features

Industrial Precision: The 0.1% accuracy span makes it suitable for processes where even a half-degree deviation can ruin a production batch.

Fast Sampling: The 10Hz sampling rate allows the PID algorithm to react quickly to thermal disturbances, ensuring a stable setpoint.

Specialized OEM Firmware: Many 996D units feature custom codes (like CUGR or NSRG) which signify factory-tuned parameters for specific semiconductor manufacturing equipment.

Robust Diagnostics: Includes comprehensive error reporting for sensor breaks, reversed thermocouples, and heater failures.

4. Application Cases

Semiconductor Fabrication: Controlling single-zone bake plates and gas delivery line heaters.

Laboratory Research: Precision temperature control for incubators, centrifuges, and chemical reactors.

Plastic Packaging: Managing heat-sealing bars and shrink-wrap tunnel temperatures.

Environmental Testing: Regulating the thermal environment in small-scale stress-test chambers.

5. Other Models in the Same Series

996A: The analog-only variant (no digital display logic).

997D: The dual-channel successor (manages two loops in the same footprint).

998D / 999D: High-accuracy vertical and horizontal 1/8 DIN variants.

Modern Successor: Watlow EZ-ZONE® PM (standard 1/16 DIN replacement).

996D

6. Installation and Maintenance

Installation

Mounting: Can be mounted in a standard 1/8 DIN or 1/16 DIN cutout depending on the specific chassis. Ensure the mounting collar is tightened to prevent ingress of moisture or dust.

Wiring: Use shielded thermocouple wire for inputs. Keep signal wires away from high-voltage AC lines to prevent EMI-induced jitter in the readings.

Grounding: Ensure the controller chassis is bonded to the machine’s safety ground to protect the internal 16-bit microprocessor.

Maintenance

Display Inspection: The LED segments can dim over 10+ years of continuous operation. If segments become unreadable, the unit typically requires a front-bezel replacement or full refurbishment.

Battery/Memory: Like other units in this family, the 996D uses non-volatile memory to store PID parameters. If the unit loses its “Job” settings after a power cycle, the internal memory circuit may be failing.

Recalibration: Annual verification with a NIST-traceable millivolt source is recommended for high-precision laboratory or semiconductor applications.

7. Unique Product Description

“The Watlow 996D is the quintessential precision single-loop controller.

Built for an era where reliability was measured in decades, it provides a level of digital stability that redefined the standard for semiconductor thermal management.

It is a compact powerhouse that proves one perfectly controlled zone is better than ten poorly managed ones.”