Digital/binary sensors and switches are critical for signal monitoring and system control, and are widely used in industrial control, industrial automation, motor control, and process automation. The output of all sensors needs to be detected and monitored by the central processing unit. To achieve this, the sensor output voltage is typically detected using two high power resistor dividers in a programmable logic controller (PLC) digital input module. To isolate each sensor channel, a separate optocoupler is required. Depending on the complexity, a system often uses multiple optocouplers (Figure 1).
Figure 1: Schematic of a conventional industrial sensor monitoring system in which a resistor divider and optocoupler are used to monitor and detect the signal output from the sensor to the system PLC.
In this traditional architecture, the resistor divider consumes a large amount of power to form a circuit board (PCB) "hot spot" that requires design to support high temperature operation and increase the heat sink. Hot spots can even reduce system reliability. In addition, for high channel count modules, multiple optocoupler designs increase system cost and power consumption, wasting valuable board space. Obviously, a compact and simple isolated digital input interface will facilitate industrial production.
Simplify the digital input of the PLC
Integration can meet this requirement. It’s easy to say it! First, increase channel input and expand system capacity, but still keep the interface simple. Now, turn to digital serialization and seek to eliminate the need to isolate optocouplers. Use configurable current limit to reduce power consumption (see Figure 4). Improve error detection and make data transmission on the same simple interface very reliable. Integrating these features makes digital input functions more complete and reliable, generates less heat, consumes less power, saves space, and costs are significantly reduced.
Implementation of isolated digital input interface design
The solution to the above design goals is the Corona isolation subsystem reference design, which uses a digital input converter/serializer and a digital isolator. Corona is designed to provide front-end interface circuitry for PLC digital input modules, supporting high voltage inputs (up to 36V), power and data isolation - all integrated into 90mm & TImes; 20mm small package. The design integrates an eight-channel digital input level shifter/serializer, a six-channel data isolator, and an H-bridge transformer driver for isolated power supply design (if there is no power in the field). We further discuss the hardware and software of the design.
Hardware description
The Corona input module is shown in Figure 2, and the system block diagram is shown in Figure 3.
Figure 2: Corona Reference Design Board (MAXREFDES12#).
Figure 3: Digital Input Subsystem Reference Design Block Diagram.
In the figure, U1 is the MAX31911 eight-channel level shifter/serializer, and U3 is the MAX14850 6-channel data isolator.
In this design, the industrial digital input serializer (U1) level-shifts, signal-conditions, and serializes the 24V digital output of the sensor and switch into a CMOS-compatible signal that meets the microcontroller's requirements. The device provides a front-end interface circuit for the PLC digital input module. Compared to the traditional discrete resistor divider scheme, input current limiting effectively reduces the consumption of field power. Figure 4 shows the current-voltage relationship for a single input channel in both methods. An optional on-chip low-pass filter flexibly debounces and filters the sensor output. On-chip 8 to 1 serialization eliminates the optocoupler required for isolation. A multi-bit CRC check is sent every 8 bits of data through the SPI port to ensure reliable communication in noisy industrial environments. For greater flexibility, the on-chip 5V voltage regulator can be used to power external optocouplers, digital isolators, or other external 5V circuits.
Figure 4: Comparison of current-voltage relationships between a single design and a single input channel in a Corona (MAX31911) design.
The U3 (MAX14850) implements 6-channel data isolation in Pmod-compatible form factors. The Pmod specification allows for 3.3V and 5V modules, as well as various pin assignments. On the Pmod side, the supply voltage can be 3.3V or 5V; the voltage on the U1 side is 5V. The supported data isolation is 600VRMS.
In most cases, the U1 (MAX31911) is powered by a 24V field supply; if no field power is available, U1 can be powered by the controller side. In the latter case, the H-bridge transformer driver (U2, MAX13256) and transformer on the Corona board provide a use-level isolated power supply for the MAX31911.
Software description
The Corona design is validated by the Nexys3 and ZedBoard platforms. Project files, device drivers, and sample code for both platforms are currently available. Because the onboard Pmod compatible connector is very simple, the Corona design is easy to use for any microcontroller or FPGA development board.
to sum up
This article describes how the Corona (MAXREFDES12#) subsystem reference design provides a compact and simple isolated digital input interface for industrial control and automation applications. Corona is designed to provide eight digital input channels. Simple cascading of multiple 8-channel digital input ICs via a single SPI interface - no additional chip select lines, it is easy to increase the number of channels by a multiple of 8. Sensor data can be transferred to the PLC with a single SPI interface, eliminating the need to isolate additional channels, significantly reducing the number of isolators required in the input module. This design significantly reduces the cost, takes up less space, and has a higher channel density per unit PCB area. This design provides sample software based on the Nexys3 or ZedBoard platform.
Fully Transparent Liquid Crystal Display
Fully Transparent Liquid Crystal Display,Industrial Instrument Lcd Display,Household Appliances Lcd Display,Fire Facility Instrument Display
Dongguan Yijia Optoelectronics Co., Ltd. , https://www.everbestlcdlcms.com