Allen-Bradley 1764-28BXB MicroLogix 1500

The Allen-Bradley 1764-28BXB is a compact PLC base unit from the MicroLogix 1500 series. It integrates a 24 V DC power supply, CPU, and a combination of digital inputs and outputs in a single package. With 16 inputs and 12 outputs, including high‑speed counter and PWM outputs, this controller is suitable for small to medium automation applications requiring high‑performance I/O in a compact footprint. The MicroLogix 1500 is known for its flexibility and expandability, with support for up to four 1762 series expansion I/O modules.

Technical Specifications

The 1764-28BXB features 16 DC inputs (24 V DC sink/source): 8 standard inputs (response time 8 ms) and 8 high‑speed inputs (20 kHz) suitable for encoder or high‑speed counter applications. Outputs: 6 relay outputs (2 A, 24 V DC / 120 V AC), 4 standard FET outputs (24 V DC, 0.5 A), and 2 high‑speed FET outputs (20 kHz) for pulse train or PWM control. The CPU includes 16 KB of user program memory, 16 KB of data memory, and real‑time clock. Communication ports: one RS‑232 channel (DH‑485 protocol) and one optional second port (RS‑232 or RS‑422/485). The base unit has 16 digital I/O points and 2 analog I/O points (field‑wired). Power supply input: 24 V DC (18‑30 V), consumption 0.6 A. Operating temperature: 0‑55°C. Dimensions: 168 mm (H) × 132 mm (W) × 87 mm (D). Weight approx. 1.0 kg.

Key Features

• 8 standard DC inputs, 8 high‑speed DC inputs (20 kHz)

• 6 relay outputs, 4 standard FET outputs, 2 high‑speed FET outputs (20 kHz)

• Integrated 24 V DC power supply

• 16 KB user program memory, 16 KB data memory

• DH‑485 networking via RS‑232 (with converter)

• Real‑time clock with battery backup

• Expandable with up to 4 1762 series I/O modules

• High‑speed counter (HSC) and PWM/PTO functions

• Two built‑in analog pots (0‑10 V) for value adjustment

• Removable terminal blocks for easy wiring

High‑Speed I/O and Motion Control

The 1764-28BXB’s high‑speed inputs (I0‑I7) can be configured as a 20 kHz counter (up to 4 counters) for quadrature encoder feedback. The high‑speed outputs (O0, O1) support pulse train output (PTO) up to 20 kHz for stepper drive control, or PWM output for speed control of small DC motors. The built‑in high‑speed counter can be used for position measurement, speed measurement, or flow monitoring. This capability makes the 1764-28BXB suitable for closed‑loop positioning and speed regulation without requiring additional motion modules.

Programming and Software

The MicroLogix 1500 is programmed using Rockwell Automation RSLogix 500 (or older versions: RSLogix Micro, DOS‑based). Languages supported: ladder diagram (LD) only. The software includes file‑based addressing, up to 256 timers, counters, and control registers. Pre‑configured instructions include high‑speed counter (HSC), PID (up to 4 loops), and PWM/PTO. The controller supports online editing and data monitoring. A built‑in real‑time clock (RTC) with battery backup allows time‑based events and datalogging with time stamps.

Expansion and Networking

The 1764-28BXB can be expanded with up to four 1762 series I/O modules (digital, analog, temperature, or specialty modules), increasing the total I/O count up to approximately 256 points (including expansion modules). For networking, the built‑in RS‑232 port supports DH‑485 protocol, which can be connected to an AIC+ (Advanced Interface Converter) to create a multi‑drop network. Alternatively, a 1761‑NET‑ENI Ethernet module can convert the serial port to Ethernet/IP for connection to a plant network or SCADA system.

Applications

Typical applications include small packaging machines, conveyor control, material handling equipment, pump and fan control, and laboratory automation. The high‑speed I/O makes it particularly suited for counting applications (e.g., bottle counting), positioning (e.g., cut‑to‑length), and speed regulation (e.g., small winding machines).

Installation and Wiring

Mount the 1764-28BXB on a 35 mm DIN rail (or panel mount with optional adapter). Connect the 24 V DC power supply to the VAC/VDC+ and COM terminals. For inputs, connect sensors (NPN or PNP) to the appropriate input terminals; a common return is required for each group. Outputs: relay outputs can switch AC or DC loads up to 2 A; FET outputs (24 V DC) require an external supply. High‑speed outputs require shielded twisted pair wiring to avoid noise. Use external fuses on output circuits for protection. The removable terminal blocks allow pre‑wiring of field connections.

Environmental and Compliance

The 1764-28BXB is UL 508 and CSA certified, CE marked, and RoHS compliant. It is rated for pollution degree 2 environments (control cabinets). Operating temperature 0‑55°C, storage -25‑70°C, humidity 5‑95% non‑condensing. Vibration resistance 2g at 10‑55 Hz. The unit is IP20 protected (no protection against dust or water ingress).

Conclusion

The Allen-Bradley 1764-28BXB MicroLogix 1500 provides a compact, high‑performance PLC solution with integrated high‑speed I/O, relay outputs, and expansion capability. Its DH‑485 networking, real‑time clock, and motion control features make it a versatile choice for small to medium automation systems.