Industrial Connection Types

Detailed information about various industrial connection protocols used in HVAC and building automation systems.

RS-232 Serial Connection

Point-to-Point

Overview

RS-232 is one of the oldest serial communication standards, typically used for direct connections between a computer and a single device. It's common in older HVAC equipment as a service port for diagnostics and configuration.

Common Uses

  • Direct connection to chillers for diagnostics
  • Service interfaces on older equipment
  • Local controller configuration
  • Firmware updates for equipment

Technical Specifications

Connection Type Point-to-Point (1:1)
Maximum Distance 50 feet (15 meters) typically
Common Connectors DB-9, DB-25, RJ-45 (modified)
Standard Baudrates 9600, 19200, 38400, 57600, 115200
Typical Formats 8-N-1, 8-E-1 (8 bits, No/Even parity, 1 stop bit)
Tip: When using RS-232, always verify the baud rate and communication parameters (data bits, parity, stop bits). These must match exactly between the devices or communication will fail.
Required Hardware: RS-232 port or USB-to-Serial adapter

RS-485 Serial Network

Multi-point Network

Overview

RS-485 is a robust serial communication standard used in industrial environments for connecting multiple devices over long distances. It's a physical layer standard that supports several higher-level protocols like Modbus RTU.

Common Uses

  • Variable Frequency Drives (VFDs) communication
  • Building Automation System (BAS) field buses
  • Modbus RTU networks in industrial settings
  • Long-distance sensor networks
  • BACnet MS/TP networks (subset of RS-485)

Technical Specifications

Connection Type Multi-drop Network (up to 32 devices standard, 256+ with repeaters)
Maximum Distance 4000 feet (1200 meters) without repeaters
Common Connectors Terminal blocks, RJ-45 (modified), DB-9 (uncommon)
Standard Baudrates 9600, 19200, 38400, 57600, 76800 (MS/TP)
Wiring Twisted pair, typically labeled as A/B, +/-, or D+/D-
Important: RS-485 networks require proper termination (120Ω resistors) at both ends of the bus. Lack of proper termination or improper biasing can cause communication errors, especially over longer distances or at higher baud rates.
Required Hardware: RS-485 interface adapter or converter

BACnet MS/TP Network

Token-Passing Protocol

Overview

BACnet MS/TP (Master-Slave/Token-Passing) is a data link layer protocol that runs on RS-485 physical layer. It's specifically designed for building automation network communications and is an ASHRAE standard.

Common Uses

  • Terminal equipment controllers (VAV boxes, FCUs)
  • Building automation field level device networks
  • Rooftop Units (RTUs) and Air Handling Units (AHUs)
  • Integration with BACnet/IP supervisory networks

Technical Specifications

Connection Type Token-passing RS-485 Network
Maximum Nodes Up to 127 MS/TP masters and 127 slaves per segment
Common Baudrates 9600, 19200, 38400, 76800 bps
Wiring 3-wire RS-485 (A, B, and Reference)
Protocol Type ASHRAE Standard 135
Tip: BACnet MS/TP networks are sensitive to MAC address configuration. Each device must have a unique MAC address within the same MS/TP network segment. Address conflicts will cause communication failures.
Required Hardware: BACnet MS/TP interface card or gateway

Web IP Connectivity

Ethernet/IP Network

Overview

Web IP refers to connectivity over standard TCP/IP networks (Ethernet/WiFi), commonly used in modern HVAC controllers with built-in web servers. This allows remote monitoring and control through standard web browsers.

Common Uses

  • Building Management System (BMS) front-ends
  • Modern HVAC controllers with web interfaces
  • Cloud-connected monitoring systems
  • Remote access to building systems
  • BACnet/IP, Modbus TCP, and other IP protocols

Technical Specifications

Connection Type Ethernet/IP Network
Common Interfaces Ethernet RJ-45, WiFi
Standard Ports 80 (HTTP), 443 (HTTPS), 47808 (BACnet/IP)
Security SSL/TLS, User Authentication, Firewalls
Protocols HTTP, HTTPS, BACnet/IP, Modbus TCP, SNMP
Important: Web IP connections should always be secured, especially if accessible from outside the building network. Use HTTPS, strong passwords, and network security measures to prevent unauthorized access.
Required Hardware: Ethernet network, router/switch, network security appliances

pLAN (pCO Local Area Network)

Proprietary Protocol

Overview

pLAN (pCO Local Area Network) is a proprietary protocol used by Carel controllers. It's designed to connect multiple Carel pCO controllers together in a coordinated control network.

Common Uses

  • Chiller sequencing and coordination
  • Multiple cooling unit management
  • Connection between Carel controllers and user terminals
  • Connection between multiple controller boards

Technical Specifications

Connection Type RS-485-based proprietary network
Maximum Nodes 32 devices (address 1-32)
Maximum Distance 500 meters total network length
Wiring 3-wire connection (GND, TX/RX+, TX/RX-)
Compatible Equipment Carel pCO series controllers, user terminals
Tip: Each device on a pLAN network must have a unique address configured using the dip switches or software configuration. Most pLAN networks require termination at the endpoints using 120Ω resistors.
Required Hardware: Carel controllers, pLAN cable, Carel configuration tools