The elevator control system can be divided into two main parts: the electric traction system and the electric control system. The electric traction system consists of a power supply system, traction motor, speed feedback device, speed control device, etc. It mainly includes the main traction circuit in the vertical direction of the elevator and the switching circuit of the car box. It provides power and implements elevator speed control. 

The electrical control system, on the other hand, consists of numerous call buttons, sensors, relays for control, indicator lights, digital tubes, and core devices for the control part. The controller integrates signal acquisition, signal output, and logic control, and together with the elevator electric traction system, it realizes all the functions of elevator control. A vertical elevator control system generally consists of a logic part controlled by a controller and a speed regulation part controlled by a frequency converter. 
  
The device in the elevator provides various signals such as load, direction change, obstacle, position, speed, etc. to the control system and dragging system, and feeds the signals back to the control system to make the elevator run in a balanced way the sensor. There are more kinds of sensors applied in the elevator, and each elevator uses 2-8 sensors, such as displacement sensor, load cell, light curtain sensor, leveling sensor, speed encoder, and so on. 

The application of sensors in the elevator industry:

1. encoder: used to encode the pulley rotation to determine the elevator position.
2. Position sensors: for pulley rotation sensing; and floor position/leveling sensing.
3. Closed-loop current sensors: used in inverters for motor control. 
4. limit switches: for elevator car position sensing and buffer system switching.
5. Hall effect sensors: for elevator door position sensing. 
6. secondary Hall effect sensors: for elevator door position sensing. 
7. Limit switch: for wire rope slack control. 8.
8. magnetoresistive sensor: for elevator car position sensing.

Displacement sensors and leveling sensors are the devices for elevator leveling control and adjustment to realize automatic leveling, and the leveling must be accurate. They are adapted to the working requirements of frequent starting, stopping, adjusting, and direction changing, so that the acceleration, deceleration, and isochronous speed are smooth, the speed curve is smooth, and there is no micro-movement before arriving at the station.

Static Magnetic Grid Displacement Sensor

The Static Magnetic Grid Displacement Sensor is a combination of two parts: the "Static Magnetic Grid Source" and the "Static Magnetic Grid Scale". The "Static Magnetic Grid Source" uses an aluminum alloy pressure-sealed passive NdFeB magnetic grid to form a grid coding array; the "Static Magnetic Grid Scale" is encapsulated in a special high-strength aluminum alloy tube with an embedded microprocessor system, and uses a switching-type Hall sensor device to form a Hall coding array. The exterior of the aluminum alloy tubing is oxidation-resistant and plastic-plated. When the "static magnetic scale source" moves relatively along the axis of the "static magnetic scale", the "static magnetic scale" resolves the digitized displacement information, and directly generates digital signals with displacements higher than millimetre orders of magnitude. The digital displacement signal is generated directly from the static magnetic scale, which is higher than millimeters. By fully utilizing the resources of the embedded microprocessor, the data update speed is increased to the order of milliseconds, so that the displacement response can be adapted to motion speeds of less than 5 m/S.

Light curtain sensor

Also known as photoelectric sensors, they are applied to door machines to protect people or objects from being pinched. The photoelectric sensor sends out a beam of device that illuminates a transmitter plate or receiver installed on the other side of the elevator door. When there is an object blocking the light between, the light curtain will work to send a signal. 
Encoder, a device that converts the signal of rotational speed into an electrical signal. It has two main functions: one is to detect the real-time position of the elevator in the shaft, and the other is to detect the real-time speed of the elevator operation. 

PLC control static magnetic grating displacement sensor to realize elevator leveling control To enable the elevator to level automatically when it reaches the leveling area, there must be a set of automatic control system, that is, the automatic control device of the elevator. The control part of the device is the static magnetic grating displacement sensor. The car is in the first floor above the ground floor, the static magnetic grating source is installed in the elevator shaft and the outdoor layer parallel to each layer, the static magnetic grating ruler is installed on the car, the length of 1.2 meters, the ground floor is installed in the two static magnetic grating source for detecting whether the car is in the bottom position and the direction of movement. 

Since the operation of the elevator is based on the call signal of the floor and car. The travel signal is controlled, and the call of the floor and car is random, so the system control adopts stochastic logic control. That is, on the basis of realizing the basic control requirements of the elevator by sequential logic control, the operation of the elevator is controlled timely according to the random input signals and the corresponding state of the elevator. In addition, the position of the car is determined by the static magnetic grating displacement sensor and sent to the counter of PLC for control. At the same time, a static magnetic grating source is set for each floor to detect the floor signal of the system. 

When the elevator is directed upward, the static magnetic grating source is detected in the upward direction of the static magnetic grating scale, the holding brake opens and the elevator goes upward. When the car touches the upper forced speed change switch, the PLC internal latching relay is electrically absorbed, and the timer Tim10.Tim11 starts timing, and the duration of its timing can be set depending on the floor distance and ladder speed of the end station. After the upward forced speed change switch is operated, the elevator is changed from fast car operation to slow car operation, under normal circumstances, the elevator should stop when going up to the level. If the car does not stop and continues to go up, when the setting value of Tim10 is reduced to zero, its normally closed point will be disconnected, the slow car contactor and upward contactor will be de-energized, and the elevator will stop running. After the car touches the upper forced speed change switch, due to some reasons the elevator fails to turn to slow car operation, and the fast car operation contactor fails to release, when Tim11 set value is reduced to zero, its normal closed point is disconnected, the fast car operation contactor and the upward contactor are de-energized, and the elevator stops running. Therefore, no matter whether it is slow car running or fast car running, as long as the upward forced speed change switch sends out a signal, no matter whether the other protection switches of the end station are operated or not, the elevator can be stopped with the help of Tim10 and Tim11, so as to make the protection of the elevator end station more reliable.

Load cell
It is a device to measures the load of the elevator and provides the load signal of the elevator for the control system. 
Load cell working principle. A resistance strain gauge is pasted on the elastic sensitive element, and then, a bridge is formed properly so that the mass of the object is converted into an electrical signal. It is mainly composed of two parts, the first part is the elastic sensitive element, the pressure and mass of the measured object will be converted into the strain value of the elastomer; the second part is the resistance strain gauge as the sensing element, he will be synchronized with the conversion of the elastomer's strain into the change of the resistance value, and then output after the corresponding transformation. The miniature load cell is laid in the elevator car and the waiting area of each floor. Realization process: first lay the sensor in the car and the waiting area under the floor, and then in the sensor's pressure probe directly above the laying of the rigid light board and balance the elastic device, and again in the light board on the lightweight carpet, to protect the sensor from damage, and finally by the signal line will be the value of the pressure signal into the signal input of the microcontroller.