Displacement sensors can output signals such as voltage signals, two-wire current signals, three-wire current signals, digital signals, and pulse signals. The wiring methods for the PLC differ depending on the type of signal output.
Commonly used displacement sensors in daily industrial production output signals include: voltage signals, two-wire current signals, three-wire current signals, digital signals, and pulse signals. The wiring methods for displacement sensors to a PLC differ depending on the signal output. Analog signals need to be isolated, amplified, and converted before being input into the PLC data acquisition system; digital displacement sensors are traditional voltage-type displacement sensors that have been modified by adding an A/D conversion module or circuitry to output digital signals or digitally encoded signals, which can be connected to the PLC through a digital input port; pulse signal displacement sensors are connected to the PLC through a high-speed counting port.
1. Displacement sensor (analog signal output) + analog signal amplifier + PLC analog input module
Resistive linear displacement sensors (electronic rulers for injection molding machines) operate on the potentiometer principle; the output voltage signal is the same as the voltage range provided by the power supply. If the displacement sensor uses a 24V power supply, it requires a 0-5V, 0-10V, or 4-20mA analog signal amplifier before being connected to a PLC analog input module. For draw-wire displacement sensors (excluding resistive output types), magnetostrictive displacement sensors, LVDT displacement sensors, eddy current sensors, etc., which can output standard analog signals, no additional analog signal amplifier is needed; they can be directly connected to a PLC analog input module.
2. Displacement sensor (digital signal output) + PLC serial communication port
Digital signal output displacement sensor solutions eliminate the need for the PLC's analog input module, utilizing the Modbus protocol for signal acquisition and allowing multiple displacement sensors to be connected in parallel simultaneously. However, due to the limitations of serial communication speed, the system response time is relatively long (typically tens of milliseconds), making it unsuitable for high-speed measurement applications.
3. Displacement sensor (pulse signal output) + PLC high-speed pulse counting port
The pulse output displacement sensor solution eliminates the need for the PLC's analog input module, while also enabling long-distance transmission, strong anti-interference capabilities, easy isolation, and fast signal response. It is widely used in the automation industry.
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