Used Industrial Controllers & PLCs for Sale

A programmable logic controller (PLC) is a ruggedized digital computer designed for industrial automation - monitoring inputs (sensors, switches) and controlling outputs (motors, valves, actuators) in real time. PLCs are used in manufacturing, automotive assembly, food and beverage processing, semiconductor fab equipment, water treatment, and power utilities. Unlike a PC, a PLC runs a deterministic scan cycle and is designed to operate continuously in environments with dust, vibration, and electrical noise. Brands in our inventory include Rockwell Automation (Allen-Bradley), Siemens SIMATIC, OMRON, and GE Fanuc.

A laser diode controller (LDC) provides precision constant-current drive and temperature stabilization for laser diodes and superluminescent LEDs used in optical fiber, photonics, and spectroscopy applications. The current must be stable to microamps to avoid mode hopping and wavelength shift; the temperature must be stable to millikelvins for wavelength-sensitive work. ILX Lightwave LDC-3900 series and ThorLabs ITC series are the two most widely used platforms in research and commercial photonics labs. The LDC-3916 mainframe accepts interchangeable plug-in modules for driving multiple lasers from one chassis.

Allen-Bradley Logix5000-based PLCs (ControlLogix, CompactLogix) use Rockwell Studio 5000 Logix Designer. Siemens SIMATIC S7-300/400 uses STEP 7 Classic; S7-1200/1500 uses TIA Portal. OMRON CJ/CS series uses CX-Programmer (part of CX-One). GE Fanuc Series 90 and VersaMax use Proficy Machine Edition. Most of these software packages are available on subscription or one-time license; some older versions are available free from the manufacturer for legacy maintenance work.

CompactRIO (cRIO) is a National Instruments embedded controller that combines a real-time processor with an FPGA in a rugged chassis, programmed using LabVIEW FPGA. It is used for high-speed control, custom signal processing, and hardware-in-the-loop testing. CompactFieldPoint (cFP) is an older NI distributed I/O platform for slower process measurements and control - temperature, voltage, current - over Ethernet. Both platforms are common in research labs, university test benches, and industrial prototyping.

A temperature controller compares a measured temperature (from a thermocouple or RTD) to a setpoint and drives a heater or chiller output to minimize the error. Simple on/off controllers cycle the output fully on or off, which causes temperature oscillation. PID (proportional-integral-derivative) controllers calculate a variable output that reduces overshoot and holds the temperature closer to setpoint - necessary for processes where ±0.5 °C stability matters. Watlow, Eurotherm/Schneider, Omega, and OMRON temperature controllers in our inventory are PID-capable. The Watlow 988 and Eurotherm 2116 series are widely used in thermal test chambers and semiconductor process equipment.

Yes, with a few precautions. The firmware version of the replacement PLC must match or be compatible with your existing program. Allen-Bradley ControlLogix modules are generally backward-compatible within a revision range, but you should confirm the series letter and firmware revision before swapping. OMRON and Siemens PLCs are similarly revision-sensitive. Battery-backed memory modules should have the battery tested or replaced. We test power-on and basic I/O function on all PLCs before listing; if you need a specific firmware version confirmed, contact us before ordering.

A variable frequency drive (VFD) controls the speed of an AC induction motor by varying the output frequency and voltage. VFDs are used where speed control matters but precise position is not required - pumps, fans, conveyor belts. A servo controller (servo drive) provides closed-loop position and velocity control for a servo motor using encoder feedback, enabling precise positioning, fast acceleration, and torque control. Yaskawa products in our inventory include both VFDs (Varispeed/A1000 series) and servo drives (Sigma series). Use a VFD for speed control; use a servo system for precision motion.