QCA-T503 Application Controller

COSYS Building Controls


Our COSYS Application and System Controls work along with our enterprise software platform OspreyFMS to provide a meaningful context.

The QCA-T503 is a fully programmable, Native BACnet™ Advanced Application Controller that communicates on an RS-485 LAN using the BACnet MS/TP protocol. The QCA-T503’s attractive housing includes a LCD display with a wide-angle view and an intuitive keypad.


  • Fully programmable in GCL+
  • Native BACnet firmware
  • BACnet MS/TP communications
  • 4/8/16 button keypad
  • Programmable LCD
  • Application database can be flash loaded over the network
  • Controller firmware can be flash loaded over the network
  • Derived Network Addressing (DNA) for simple integration into a standard network architecture
  • Expansion I/O subnetwork
  • Service port


The QCA-T503 is suitable for various room applications with small I/O requirements such as Fan Coil Units, Unit Ventilators and Heat Pumps. Because of its programming capability, the QCA-T503 can be used to create or modify GCL+ programs and BACnet objects for specific applications.


BACnet Device Profile
BACnet Advanced Application Controller (B-AAC)
Large font 4-digit alpha numeric display (for time, object value or units)
Small font 4-digit alpha numeric display (for time or units display)
12-digit alpha numeric display (for object names, menu commands or options)
10 display icons representing different
4, 8 or 16 buttons (suitable for different applications)
Security door
Temperature Sensor
Thermistor Input - 10kΩ at 77°F (25°C)
Accuracy +/-0.4°F from 32 to 158°F
(+/- 0.2°C from 0 to 70°C)
Display resolution of 0.1°
Stability 0.24°F over 5 years (0.13°C)
External Inputs
3 Universal inputs - 10 bit (supporting 0-5v,
0-10v, 10kΩ)
External Outputs
5 Binary FET outputs
(VAC or DC switching or PWM)
Jumper selection for internal or external power on binary outputs
32-bit processor
1 MB (8 megabit) Flash memory
127 KB SRAM memory for database
LED indication of CPU and SCAN status
Device Addressing
Set via keypad configuration setup or software setup
Communications Ports
Main LAN (NET1)
BACnet MS/TP @ 9600, 19200, 38400 or
76800 bps (default)
(NET2)  LINKnet @ 76800 bps
(maximum 4 devices on LINKnet, with no more than 2 DFM devices)
AMP plug-in terminal connectors
Class 2
24 VAC
5VA, 65VA with BOs fully-loaded
32° to 131°F (0° to 55°C)
10 - 90% RH (non-condensing)


Order the QCA-T503 with the desired options according to the following product numbers:
QCA-T503-xxx—Controller, No Backlighting
xxx—Append the keypad code to specify the desired buttons