High Current Heater Control – Embedded Hardware Design

MZHP – “Multi-Zone High Power” Temperature Control Module

Graco recently released the new Reactor Generation 2 proportioner system used to dispense spray foam insulation and polyurea coatings (for truck bed liners, coatings for oil pipelines, etc.). A large engineering team worked hard to redesign the original Graco Reactor proportioner system from the ground up, including complete redesign of the electrical control systems.

The Multi-Zone High Power (MZHP) temperature control module was one newly designed piece of hardware within this project. It was designed within the Graco Control Architecture (GCA) platform which offers the company the many benefits of embedded code and circuit reuse.

This module’s purpose was to support the operation of two 10 kW material heaters and a 4 kW heat-wrapped hose bundle. The unit operates on a Microchip based PIC24 microcontroller with RTOS (Real Time Operating System) based applications. Design timeline was approximately 18 months.

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DESIGN RESPONSIBILITIES:

Art Graf oversaw the embedded and mechanical hardware design including:

• Development of CRD (Customer Requirements Document) with Commercial team
• Specification and sourcing of all (non-platform specified) components including triacs, 50A relays, connectors, cooling fan, custom heat sink
• Special focus circuit designs:
  • 24 to 5 VDC switch mode power supply layout
  • Current-Limiting Impedance voltage measurement circuit
• PCB design (Altium Designer) of 50 Amp, 240 VAC rated (4 oz. copper) circuit board and control-level (3.3, 5, 24 VDC) circuit board.
• Life-testing, HALT (Highly Accelerated Life Testing), Environmental (heat, humidity, etc.), power disturbance (surge/sag/etc.) testing.
• Overall mechanical design including custom heat sink and sheet metal components, form factor, labeling, tolerance stack-ups, etc.
• Approvals (Intertek/ETL) under UL 508 (Standard for Industrial Control Equipment)

Art also assisted with software/firmware development and EMC pre-testing, design troubleshooting, and full-compliance testing.