NHM 393 – Net Heat Calculator

Short description: A rugged microcontroller-based Net Heat Calculator for Building Automation, designed for chilled water systems. Accepts flow and temperature inputs, computes instantaneous net heat, and provides 8-digit totalisers with RS485 MODBUS RTU communication.

Key Features

• Compact, rugged microcontroller-based system.
• Accepts three 4–20 mA inputs: Flow, Inlet Temperature, and Outlet Temperature.
• Calculates instantaneous Net Heat using density and enthalpy tables.
• Displays Flow, Temperatures, and Net Heat on backlit LCD.
• 8-digit Net Heat and Volumetric Flow totalisers with real-time clock support.
• Programmable flow rate span and RS485 parameters via keypad.
• Password protection for all settings.
• RS485 MODBUS RTU communication for integration with SCADA/BMS.
• LED indications for serial communication.
• Non-volatile memory stores all settings and totaliser values.
• 24VDC, 100 mA excitation supply for external temperature transmitters.
• Ideal for centralized air conditioning and building automation applications.

Technical Specifications

• Inputs: Three 4–20 mA (Flow, Inlet Temperature, Outlet Temperature; up to 21.6 mA)
• Accuracy: ±0.25% of FSR ±1 bit (instantaneous), ±1% of value (totalisers)
• Display: 16 × 2 backlit LCD for Flow, Temperatures, Net Heat
• Keyboard: 4-key tactile keypad
• Resolution: 12-bit ADC
• Totalisers: 8-digit for Net Heat & Volumetric Flow
• Real Time Clock: Ensures accurate totaliser values
• Settings: Programmable flow rate span, communication, and logging interval (1–240 sec/min/hr)
• Password Protection: For all programming and data access
• Communication: RS485 port with MODBUS RTU protocol
• Excitation Supply: 24VDC, 100 mA for transmitters
• Power Supply: 230 VAC, 50 Hz ±10% (optional 110 VAC)
• LED Indications: For serial communication
• Cabinet: Rugged ABS, panel mount
• Dimensions: Bezel: 96 × 96 mm; Depth: 110 mm; Cut-out: 92 × 92 mm
• Connections: Screw-type connectors on rear

Support Videos

Downloads

• 📄 Product Manual (PDF)

Need More Help?

Call us at +91-20-24479210 or email scan@vsnl.com

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