| AC |
Alternating current. Current that periodically reverses direction. |
| address |
The unique identifier assigned to each component of a PLC system to permit communication throughout the system. |
| alternating current |
AC. Current that periodically reverses direction. |
| analog signal modules |
Signal modules designed for use with variable voltage or current signals. |
| backplane |
A part of a PLC rack that provides communication paths for installed modules. |
| binary |
The most commonly used number system in PLCs and other computer systems, also known as the base 2. Each position in a binary number represents a power of 2. The binary system has only 2 characters, 0 and 1. |
| bit |
A single character represented by a 0 or 1 in a binary value. |
| bus |
A set of conductors or signal wires shared by multiple modules or devices. |
| byte |
Eight bits. A bit is a single 1 or 0. |
| central processing unit |
CPU. The main device that processes information and carries out instructions in a PLC. Also known as the processor or controller. |
| channel |
Each connection point for an input or output on a signal module. |
| CPU |
Central Processing Unit. The main device that processes information and carries out instructions in a PLC. Also known as the CPU, processor, or controller. |
| DC |
Direct current. A current formed when electrons flow in one continuous direction. |
| device addresses |
Device identifiers used to identify programmable modules with interfaces to a network. |
| DIN rail |
A metal track or rail to which PLCs and other control devices can be easily attached or removed. |
| direct current |
DC. A current formed when electrons flow in one continuous direction. |
| discrete input device |
An input device that has only two operating states, on or off. A pushbutton is an example of a discrete input device. |
| discrete signal module |
Signal modules designed for use with discrete on or off signals. |
| distributed I/O |
PLC I/O system components mounted in remote locations from the CPU. |
| flow switches |
Switches that detect the movement of any fluid, such as liquid, gas, or air in a system. Flow switches are sometimes used as discrete input devices for PLCs. |
| heating element |
A device that heats a component when activated. Heating elements are sometimes used as discrete outputs for PLCs. |
| HMI |
Human machine interface. A device connected to a PLC to allow operation and maintenance personal to monitor and control a machine or process. |
| I/O addresses |
PLC addresses used to identify signal modules to allow the CPU to read inputs and control outputs. |
| I/O system |
Input/output system. A system that translates the signals received from input devices into low-voltage DC signals that the CPU can recognize and performs the reverse operation when the CPU sends signals to output devices. |
| input device |
A sensor that sends information to a PLC. Input devices are connected to PLC input modules. |
| input/output system |
I/O system. A system that translates the signals received from input devices into low-voltage DC signals that the CPU can recognize and performs the reverse operation when the CPU sends signals to output devices. |
| installation |
The process wiring and preparing a system for use. |
| LED |
Light emitting diode. A semiconductor device that emits light and is often used as an indicator on electronic equipment. |
| level switches |
Switches that detect the height of a liquid or solid in a tank or another type of vessel. Level switches are sometimes used as discrete input devices for PLCs. |
| light emitting diode |
LED. A semiconductor device that emits light and is often used as an indicator on electronic equipment. |
| limit switches |
A type of sensor that requires physical contact to detect the presence or absence of an object. Limit switches are sometimes used as discrete input devices for PLCs. |
| load current power supply |
Provides power to input and output devices and related circuits. Also referred to as the load power supply. |
| load power supply |
Provides power to input and output devices and related circuits. Also referred to as the load current power supply. |
| modules |
Removable system assemblies. For example, of a modular PLC is made up of a CPU module, I/O modules, etc. |
| motor starter |
A device that starts and stops a motor. Motor starters are sometimes used as discrete output devices for PLCs. |
| output device |
An actuating device is controlled by signals from a PLC output module. |
| parameter |
Settings that specifically define a module's operational characteristics. |
| photoelectric switches |
Switches that use a light beam to detect the presence of an object without touching it. Photoelectric switches are sometimes used as discrete input devices for PLCs. |
| PLC configuration |
The process of arranging, setting, and networking PLC devices and modules. For a Siemens PLC, this is done primarily using Step 7 engineering software. |
| PLC tag table |
An area of a PLC's CPU where the various tags are stored. |
| PLC tags |
The symbolic names for various memory addresses in a PLC. |
| polarity |
The direction of current flow. When using DC inputs, the polarity must match between the input and the module. |
| power budget |
The amount of power available from a power supply. |
| pressure switches |
Switches that detect applied pressure and activate electrical contacts and turn on or off in response to the amount of pressure applied. Pressure switches are sometimes used as discrete input devices for PLCs. |
| process image |
The area of CPU memory where input and output status information is stored. |
| PROFIBUS |
An set of open field bus standards of PROFIBUS & PROFINET International that allow control-level automation devices to communicate with each other. |
| PROFINET |
An open standard of PROFIBUS & PROFINET International that allows both control and IT communication. PROFINET is the most widely used form of Industrial Ethernet. |
| proximity switches |
Switches that use an electronic sensing field to sense the presence of an object without touching it. Proximity switches are sometimes used as discrete input devices for PLCs. |
| pushbutton |
A type of switch that is operated by someone pressing it. Pushbuttons are sometimes used as discrete input devices for PLCs. |
| relay |
An electromechanical or solid state device controlled that can be controlled by a PLC output or a similar device used on a PLC output signal module. |
| relay modules |
A type of PLC output module with relay contacts that can be used with either AC or DC output devices. |
| resistance temperature detector |
RTD. Temperature sensors that contain a resistor that changes resistance as its temperature changes. Also known as a resistance thermometer. |
| resistance thermometer |
RTD. A temperature sensor made from a metal such as platinum, nickel, or copper that varies in resistance in a predictable manner as temperature varies. |
| resolution |
The number of bits used by an analog input or output channel. Higher resolution analog input channels allow for a greater amount of information to be sent to or received from devices. |
| RTD |
Resistance temperature detector or resistance thermometer. A temperature sensor made from a metal such as platinum, nickel, or copper that varies in resistance in a predictable manner as temperature varies. |
| signal modules |
Input/output modules in Siemens PLCs. |
| sinking connections |
A PLC DC I/O module connection polarity. |
| solenoid |
A type of output device coil that converts electrical energy into mechanical energy via magnetic fields to exert a force, typically in a linear direction. Some solenoids are used as discrete output devices for PLCs. |
| sourcing connections |
A PLC DC I/O module connection polarity. |
| STEP 7 |
Engineering software designed by Siemens for use with Siemens PLCs and related devices. |
| system power supply |
Converts the incoming power to a low-voltage DC power while also filtering and regulating it |
| temperature switches |
Switches that react to different heat intensities and activate electrical contacts when the temperature rises or drops below a set level. Temperature switches sometimes used as are discrete input devices for PLCs. |
| thermocouple |
A temperature sensor made from two dissimilar metals joined at a point called a junction. A thermocouple produces a small voltage that is temperature dependent. |
| TIA Portal |
Engineering software that includes STEP 7 as well as other software for use with PLCs, HMIs, Drives, and related devices. |
| triac |
An electronic switch that allows small control voltages and currents to switch larger AC voltages. Triacs are often used in PLC AC output signal modules. |
| valve |
A mechanical device by which the flow of liquid, gas, or other objects may be regulated by moveable parts that open, close, or obstruct one or more openings or passageways. Some valves are controlled by PLC outputs. |
| voltage |
Electrical force, also referred to as electromotive force. Voltage is necessary to cause electrical current to flow in a circuit. |