Common Switch Communication Interface of Flowmeters

Outline of this Article

● What is a Switch Signal?

● Reed switch

● Electromagnetic Relay

● Transistors

● Other logic output interface



What is a Switch Signal?


For example, lights have ON and OFF. The switch signal changes the ON, OFF to 1, 0 format, arranging it into a meaningful series in time (similar to Morse code) then transmits it to the external device and achieve system control through the digital communication.


The pulse output types provided by the flowmeter include reed switches, transistors (NPN and PNP interfaces), logic devices, Namur sensors (current pulses) and solenoids, and this article will introduce several common switch communications.


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➤ Reed switch


The principle of the reed switch


The reed switch structure consists of two magnetic reeds sealed in a glass tube, and the contact ends are plated with wear-resistant, tougher metals (usually rhodium and ruthenium) to increase service life. In order to prevent the metal magnetic reed from being oxidized, the glass tube is usually filled with an inert gas, and what's more is that the gas in the glass tube is evacuated to a vacuum state thus, its efficiency is further improved.


The principle of the reed switch is very simple. The most basic and common reed switch is shown in the figure above. When a magnetic field is close to the two magnetic reeds, the magnetic attraction force is greater than the elasticity of the magnetic reeds themselves, and the two magnetic reeds will be attracted to conduct conduction. However, because the reed switch is small and delicate, the smaller the resistance, the greater the resistance, and it cannot run too much current, so it has its limitations in use. In addition, based on industrial manufacturing errors, reed switches are usually only used to transmit basic status information, such as LORRIC's inductive variable area flowmeter; the signal output of its digital limit signal is based on this principle to operate. The anti-theft system of doors and windows is one of the most common applications of reed switches in life. After the resident closes the doors and windows, the anti-theft system is activated.


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➤ Electromagnetic Relay


Electromagnetic Relay


Electromagnetic relay is an automatic switch that uses small electric current to control large electric current. Its principle is very similar to that of a reed switch, but it is different from a reed switch in that it changes the permanent electromagnet into an electromagnet. When the electromagnet is energized, the iron core in the coil will generate an electromagnetic force, which moves the common contact and conducts its device.


In addition, electromagnetic relays can be used to conduct large electrical currents or to completely isolate them. Direct operation of high-current electronic equipment will produce certain dangers, electromagnetic relays are used for indirect operation to ensure safety.


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➤ Transistors





Transistors are also called "contactless switches''. In general, switches with contacts will experience wear and tear or other problems with their contacts from switching circuits for a long period of time. The invention of the transistor solves the defects of the switch with contacts. The conductivity of semiconductors is between conductors and insulators, and can be changed by other electrical signals, and transistors use the characteristics of semiconductor materials themselves that can change from insulators to conductors, and then control the ON and OFF arrangements through other external electrical signals into a temporarily meaningful sequence, and transmit it to an external device.


The transistor has no mechanical structure composed of magnets and reeds, so the signal transmission speed is faster. In addition, the transistor can also transmit more signals, not limited to the state. LORRIC's patented AxleSense paddle wheel flowmeter is equipped with OCT, one of the wired communication parties, which operates on the above principle. In addition, LORRIC's products also have further optocoupler protection. When the factor is damaged, other functions of the device can continue to operate normally without being affected by it.


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➤ Other logic output interface


Other logic output interface



The logic output is no longer a switching signal, but a simple logic signal, which is generally switched between two predetermined voltage levels. The two voltages are respectively defined as logic 0 and logic 1. When the output voltage is lower than the set value, a signal of 0 will be sent out, on the contrary, when the output voltage is higher than the set value, a signal of 1 will be sent out.


The most common definitions of logic output interfaces are TTL and CMOS. TTL defines logic 0 (output below 0.4V) and logic 1 (above 2.4V), typically 0 is a few millivolts and 1 is closer to 5 volts. CMOS is defined relative to the internal supply voltage (typically 3.3V or 5V) as 0 below 33% of the supply voltage and 1 above 66%. Therefore, when the voltage is lower than 33%, a signal "0" will be sent out, and conversely, when the voltage is higher than 66%, a signal "1" will be sent out.


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