The sensors serve as a bridge that connects the physical environment and the electrical/electronic devices for industrial purposes. These devices have a wide range of applications such as control, protection, and imaging during the industrial process.
Hundreds of types of sensors produced today can be mentioned. Incredibly fast developments in micro-electronics technology enable you to develop a new invention or a new type of application every day.
In technical terminology, the terms of the Sensor and transducer are frequently used in place of each other. The transducer is generally defined as the energy converter. The Sensor is a device that converts various energy formats into electrical energy. In 1969, however, the ISA (Instrument Society of America) recognized these two terms as synonyms and described it as "a tool that converts the measured physical properties, quantities, and conditions into an available electrical amount".
Classification of sensors
It is possible to separate the sensors into many different classes. According to the measured size, according to the size of the output, according to the requirement of feeding etc...
By entry sizes
The size measured by the sensors can be divided into 6 groups. These;
1. Mechanical: Length, area, quantity, mass flow, force, torque (moment), pressure, velocity, acceleration, position, sound wavelength and intensity
2. Thermal: temperature, heat flux
3. Electrical: Voltage, Current, çarc, resistor, inductance, capacitance, dielectric coefficient, polarization, electric field, and frequency
4. Magnetic: field density, flux density, magnetic moment, permeability
5. Glow: Density, wavelength, polarization, phase, projection, sending
6. Chemical: condensation, content, oxidation/redaction, reaction rate, PH quantity
According to the output sizes
On the other hand, digital outputs that are alternative to analog outputs can communicate directly with computers. Certain protocols are used when establishing these communications. The serial communication protocols are mentioned briefly below.
RS232C: This protocol was originally designed for phone data communication. Then many computer systems started using it frequently, and ultimately RS232 has become a standard communication protocol. RS232C's work should end in one (single-ended). Logic is between 1 =-15.0-3 and logic 0 = + 3, + 15. Sensors send data to the computer in bits and in accordance with the serial communication protocol. Since RS232C is a single-ended interface, the distance between the receiver and the sender should be kept short in terms of reducing negative factors (EMI, RFI interference) from the external environment.
RS422A: This protocol has a differential ended interface. The distance between the transceiver is far enough away. The system will continue to communicate even if the attenuation is reduced to a level of 200mv due to this distance. Thanks to the differential interface, the signal attenuation is negligible and can be provided with a very high data rate. In communication between the sensor and the computer, the Twisted Pair (twisted cable) is used to interact with external influences.
RS485: Standard 422a is a protocol that is created by extending the protocol. The 32 receiver transmitter can work with this Protocol to provide data communication with a single cable. The RS485 protocol eliminates communication problems on the cable.
Output interface type Max cable length max Data rate communication type RS232C Single ended voltage 15 Mt 20kbps point to point RS422A differantial voltage 1.2 km 10mbps point to point RS485A differantial voltage 1.2 km 10mbps multidrop (32 Node) Table 2: Serial communication Protocols
According to the requirement of feeding
Sensors can be divided into two classes according to their supply requirement. These;
Passive sensors
They convert physical or chemical values to another size without receiving external energy (without the need for supply voltage) in any way. Examples of this sensor type are thermocouple (T/C) or switches. T/C will be explained below. The key is to convert a mechanical movement into an electrical ignition as known.
Active sensors
They need an external energy diet for their work. These sensors are typically used to measure weak signals. The points to be considered in active sensors are inputs and outputs. These types of sensors produce electrical output signals in digital or analog format. In Analog outputs, the output size is voltage or current. Voltage output is generally used fairly widely in the range of 0-5v. However, the 4-20ma current output has now become the standard in the industry. In some cases, the current cycle of 0-20ma is used, but in cases such as disruption to the industry often occurring in the lines, the system is easier to detect and 4-20ma is more common in order to make data communication healthy. Very old sensors have 10-50 MA current outputs. The use of the most widely used 4-20 MA cycle type in the industry requires some special occasions.
These points are;
• No electrical supply voltage is required at remote points where the sensors are placed.
• Sensors should be used in hazardous applications where the voltage signal may be limited!
• The cables to the sensor must be limited to two.
• The current cycles are relatively protected against sudden jumps of the noise voltage. However, it cannot transmit long-distance data.
• Sensors must be electrically insulated from the measuring system.