Whether used for process control installation or industrial automation system, I / O module or field junction box faces various unique challenges in the whole product life cycle. Product management needs to decide how many channels to use and what combinations to make for each product. Electronic designers must decide how to achieve excellent performance and cost-effective systems for various analog or digital signals in the project. All different products and a large number of wiring diagrams may strain the installation technician. If we can design a highly flexible system to deal with these problems, will life be easier?

Whether used for process control installation or industrial automation system, I / O module or field junction box faces various unique challenges in the whole product life cycle. Product management needs to decide how many channels to use and what combinations to make for each product. Electronic designers must decide how to achieve excellent performance and cost-effective systems for various analog or digital signals in the project. All different products and a large number of wiring diagrams may strain the installation technician. If we can design a highly flexible system to deal with these problems, will life be easier? ADI's new product family software configurable input / output (swio) IC can achieve this goal. It can support almost any function and combination on the pin at any time.

For industrial programmable logic controller (PLC) or distributed control system (DCS) in process control or factory automation, the requirements of end customers and applications are different. It is a difficult task for product managers to define the right products, strategies and optimization. 1 one end customer may need more analog output channels, such as 4 mA to 20 mA, while another end customer may need more digital inputs. Or one platform of this customer needs more analog channels, while the other platform needs more digital channels. An example of this dilemma is shown in Figure 1. With the emergence of industry 4.0, consumer behavior and demand have also changed. Therefore, manufacturers need more flexible systems to quickly and easily adapt to changing requirements. To this end, manufacturers can no longer rely on fixed large-scale systems and predictable needs designed for mass market products. Instead, they need flexible systems that support rapid reconfiguration with very low levels of downtime and capital investment.

Figure 1. Number of channels and configuration possibilities.

Swio components support not only their channel programming as input or output, but also analog or digital programming. In addition, they can be set up efficiently to read 2-wire or 3-wire RTDS or thermocouples.

Since the software configurable I / O can be further used for brownfield devices that need to be updated to 10base-t1l Industrial Ethernet system, it can be used as a connection bridge between Ethernet based control networks. It also supports the development of standardized configurable field I / O units that can support Hart in existing systems ® The 4 mA to 20 mA sensor and actuator are converted to 10base-t1l or 100m fiber return.

Figure 2 shows the four channel swio device ad74413r, which is designed to meet process control, factory automation or building control applications (this paper focuses on industrial applications). This device is a fully integrated overall solution for industrial input and output operations. The ad74413r has a 16 bit, ∑- Δ ADC and four 13 bit DACs with 9 mm supporting an operating temperature range of – 40 ° C to + 105 ° C × 9 mm, 64 pin lfcsp package. Each channel is configured by writing the configuration register through SPI bus with clock up to 24 MHz. The user can improve the default configuration of each operation mode through the ad74413r register diagram.

Figure 2. Software configurable I / O components and typical application examples.

16 bits of ad74413r Σ-Δ The ADC can measure current or voltage on one or more of the four channels and up to four diagnostic inputs through a single conversion request. The conversion rate is up to 4.8 ksps and optional 50 Hz and 60 Hz suppression filters are provided.

The 13 bit R-string DAC per channel is monotonically linear in nature. These DACs support current outputs up to 25 mA and have open circuit detection capability for fault diagnosis. Similarly, a true voltage output of 0 V to 11 V can be provided.

The ad74413r has a high-precision internal reference voltage source to drive DAC and ADC in price sensitive applications. However, when high performance is required, an external reference voltage source can be used.

Possible functions and modes of operation

The functions of each channel are summarized in Table 1. The component can support voltage output, current output, voltage input, externally powered current input, loop powered current input, external RTD measurement, digital input logic and loop powered digital input. After power on or device reset, there is also a high impedance mode as the default function.

Table 1. Possible function options

The voltage output amplifier can produce unipolar voltages up to 11 v. The internal low voltage charge pump allows the amplifier to produce a true zero output voltage. In this mode, the external detection resistance provides current feedback (pressurized current measurement fvmi method) through sensor_ The negative feedback of the x pin regulates the correct voltage level.

In the current output mode, the current output (usually 0 Ma to 25 mA) provided by the DAC is adjusted by detecting the differential voltage on the sensor resistance (sensor_x and senseh_x pins). In order to reduce the power consumption on the bare chip under low resistance load, an external PMOS can be connected to output current from 0 Ma to 25 mA.

Current input mode can support external power supply and loop power supply configuration. 16 bit Σ-Δ ADC automatically measures current by detecting resistance. The filterable detection pins (sensehf_x and senself_x) are used for this purpose. In addition, both types of current input functions have additional Hart compatible modes that ensure a minimum 230 Ω receiving impedance. two

The voltage input mode uses the ADC to measure the voltage through one of the filter ports (senself_x) and the ground inductance. Additional pull-down options can be selected for floating voltage. In voltage input mode, thermocouple readings can also be obtained through the special range setting in the ADC.

The resistance measurement mode uses a voltage obtained from a 2.5 V bias voltage to bias the external 2-wire RTD. Accurate ratio measurement can be ensured by pulling up the resistance to the bias voltage. Low excitation current can minimize power consumption, so as to reduce the self heating of RTD.

The digital input mode supports IEC 61131-2 type I, type II and type III devices. The threshold can be programmed through a dedicated register. Each channel has a dedicated general purpose output (GPO) and user programmable anti shake filtering.