Automation and Control Selection Guide

Automation products are grouped by the sensing, decision, drive and operator interface layers of a panel; the choice is made according to the function needed.

This guide explains what to look at when choosing products in the Automation and Control category.

The layers of an automation panel

The subcategories correspond to the functional layers in a machine or process panel.

• Sensing and measurement: Industrial Sensors (inductive, capacitive, photoelectric), plus the temperature probes, temperature controllers and panel-type measuring instruments under Measuring and Control Devices.
• Decision: PLC Systems with PLC Input and Output Modules; control relays such as timer, liquid level and photocell relays for single-function tasks; motion controllers for multi-axis machines.
• Drive: Variable Frequency Drives (Frequency Inverters), soft starters, Servo Systems and stepper motor systems.
• Operator interface: Control Push Buttons, Switches and Pedals, pilot lights and signal towers, HMI and operator panels, panel PCs.
• Infrastructure: power supplies that provide the control voltage, automation relays and solid state relays that isolate the signal from the load, communication hardware that connects devices to the network, SCADA and automation software.

Choosing a controller: control relay, smart relay or PLC

• For a single, fixed function (delay, level, twilight), a standalone control relay is enough; it requires no programming.
• In small machines that build simple logic with a few inputs and outputs, DIN rail smart relays and mini PLCs with a display are used; this group includes, for example, models with 12 digital inputs and 8 relay outputs.
• If analog measurement, communication, many inputs and outputs or axis control is needed, a modular PLC is selected; digital, analog, temperature, load cell and communication modules are added to the CPU.

Determine the number of inputs and outputs by leaving room for signals to be added later. Decide the output type according to the load: a relay output switches AC and DC loads, but its switching speed and mechanical life are limited; a transistor output drives only DC loads, produces fast pulses, and is required to send a pulse signal to a stepper or servo drive.

Signal compatibility

The wiring type of the sensor output and the PLC input must complement each other. An NPN-output sensor pulls the input to negative; for this, the common terminal of the input group must be connected to positive. A PNP-output sensor supplies positive to the input; the common terminal is connected to negative. Manufacturers call these two connections sink and source, but they do not use the names in the same direction: in one manufacturer's manual, the module that matches an NPN sensor is called a sourcing input, while in the Delta DVP-SA manual the same connection, where current enters the S/S common terminal, is called sink. For this reason, look at the polarity of the common terminal in the module diagram, not at the name.

For analog signals, match the signal type (voltage or current) and range the module accepts, and for temperature measurement the probe type (for example NiCr-Ni (K) thermocouple or PT100), to the input type of the module or controller. For push buttons and limit switches, the contact arrangement is written in the product name as 1NO, 1NC or 1NO+1NC.

Soft starter, frequency inverter or servo in motor control

• A soft starter only softens starting and stopping; once the motor has started, it runs at mains frequency and constant speed.
• A frequency inverter (variable frequency drive) adjusts the motor speed throughout operation; it is used with loads whose speed varies with the process, such as pumps, fans and conveyors. This group also includes braking resistors, solar pump drives and drive accessories.
• A servo system performs position, speed and torque control with encoder feedback; the motor and drive are matched from the same series.
• A stepper motor is mostly used on lightly loaded axes with positioning without feedback (open loop).

The drive and starter are determined from the manufacturer's selection table according to the rated current on the motor nameplate and the load type; looking only at the kW value can be misleading.

Brands in this category

• Schneider Electric: push buttons and pilot lights, Altivar drives, Altistart soft starters, PLCs and input-output modules, HMI panels and SCADA software licenses.
• Isıso: thermocouples and temperature probes, power supplies, solid state relays and sensors.
• ABB: motor drives and accessories, PLC processors and modules, timer and control relays.
• EMAS: push buttons, limit switches and pilot lights.
• Siemens: 3SU1 coded push buttons and pilot lights, timer relays, communication hardware.
• Lanbao: inductive and photoelectric sensors.
• Delta Electronics: servo motors and drives, DVP series PLCs and modules, operator panels, panel PCs and motion controllers.

Order notes

Products in this section are sold per piece. A portion of the products, notably soft starters, servo systems, drives and software licenses, are listed as made-to-order; the lead time for these products is confirmed before ordering. For jobs where the part number is known, typing the manufacturer code, such as ATV930U75N4 or 3SU1150-0AB10-1CA0, into the site search is faster than browsing the category tree.

Automation and Control Equipment Comparison Table

Frequently asked questions

What is the difference between a PLC and a smart relay?

A smart relay is a small controller that combines a limited number of inputs and relay outputs in one housing, and is mostly programmed from its built-in display or with simple software; it is sufficient for pump sequencing, lighting and simple machine control. In a modular PLC, the processor is a separate CPU and it expands with modules such as digital, analog, temperature and communication. If analog control, network communication, many inputs and outputs or axis control is needed, a PLC is selected.

Can an NPN-output sensor be connected to any PLC input?

No, the wiring type of the input is decisive. When an NPN sensor switches on, it pulls its output to negative; for this, the common terminal of the input group must be connected to positive. A PNP sensor supplies positive to its output and works with an input whose common terminal is connected to negative. In input groups where the common terminal is left to the user, both types can be used, but all sensors in the same group must be of the same type. Before ordering a sensor, check the input diagram in the PLC or module data.

What is the difference between a soft starter and a frequency inverter?

A soft starter raises the motor voltage steplessly at start-up, reducing the inrush current and mechanical shock; once the motor has started, it turns at constant speed at mains frequency. A frequency inverter, on the other hand, adjusts the speed throughout operation by changing the output frequency, and also makes starting controlled. If speed adjustment is not needed and the goal is only soft starting and stopping, a starter is selected; if flow or line speed will be adjusted, an inverter is selected.

How do you choose between a servo motor and a stepper motor?

A stepper motor turns a fixed angle with each pulse from the drive and mostly positions without feedback; it is used on low-speed, lightly loaded and simple axes. In a servo system, the encoder on the motor reports the position to the drive, and the drive continuously corrects the error. If the load varies, the speed is high or loss of position is unacceptable, a servo is selected; for simple indexing jobs, a stepper system may be sufficient.

Does a PLC expansion module work with a CPU of a different brand or series?

Generally not. Expansion modules connect to the CPU through the manufacturer's own bus and connector; compatibility may not exist even between different series of the same brand. To combine devices of different brands, remote I/O modules or gateways over open communication protocols such as Modbus, CANopen or EtherCAT are used. Before ordering a module, verify the compatible CPU and series information on the product page.