What is Switch signals Communication?

Switch signals convert ON/OFF states into a 1/0 format, arranging them into meaningful sequences over time, like Morse code, to control systems digitally. Flow meters provide pulse output types including reed switches, transistors (NPN and PNP junctions), logic devices, Namur sensors (current pulses), and electromagnetic coils, and this article will introduce several common switch communications.

A reed switch structure seals two reed plates inside a glass tube, with wear-resistant, hard metal (often rhodium and ruthenium) plating on the contact points to extend lifespan. To prevent oxidation of the metal reed plates, the glass tube is often filled with inert gas, or even evacuated to create a vacuum, enhancing performance. The principle of a reed switch is simple: when a magnetic field approaches, the magnetic attraction overcomes the elasticity of the reed plates, causing them to contact and complete the circuit. However, due to their delicate nature, reed switches have inherent limitations on the amount of current they can carry.

Electromagnetic relays use a small current to control a larger one, similar to reed switches but with an electromagnet instead of a permanent magnet. When the electromagnet is energized, the core's electromagnetic force moves the common contact point to complete the circuit. They are used to handle large currents or provide complete insulation for safety reasons, as direct handling of high-current devices can be hazardous.

Transistors, or "contactless switches," address the wear and other issues associated with contact-based switches. Semiconductor conductivity, between that of a conductor and an insulator, can be altered by other electrical signals. Transistors utilize the semiconductor material's ability to switch from insulator to conductor, controlled externally to manage ON (conducting) and OFF (non-conducting) states. Without the mechanical structure of magnets and reed plates, transistor signals are faster and can carry more complex signals beyond mere states. LORRIC's patented AxleSense paddlewheel flow meters employ OCT for wired communication based on this principle, with further optical coupling protection to ensure other functions remain unaffected if the switch circuit is damaged externally.

Logic outputs are not switch signals but pure logic signals, typically switching between two predefined voltage levels, defined as logic 0 and logic 1. Low output voltage sends a "0" signal, and high output voltage sends a "1". The most common logic output interfaces are TTL and CMOS, defining logic 0 (below 0.4V) and logic 1 (above 2.4V) for TTL, and for CMOS, 0 as below 33% of the supply voltage and 1 as above 66%, translating to signals depending on the supply voltage's relation to these thresholds.