A design based on a complete data acquisition system

Introduction

Programmable Logic Controllers (PLCs) are at the heart of many industrial automation and process control systems that monitor and control complex system variables. PLC-based systems use multiple sensors and actuators to measure and control simulated process variables such as pressure, temperature, and flow. PLCs are used in a wide variety of applications, such as factories, refineries, medical equipment, and aerospace systems, which require high precision and maintain stable long-term operation. In addition, the fierce market competition requires lower costs and shorter design time. As a result, designers of industrial equipment and critical infrastructure have met severe challenges in meeting customers' stringent requirements for accuracy, noise, drift, speed and safety. This article takes PLC application as an example to illustrate how the highly integrated, low-cost, highly integrated ADAS3022 can reduce the complexity and solve many problems encountered in the design of multi-channel data acquisition systems by replacing the analog front end (AFE) level. With high input range, this high-performance device is ideal for high-precision industrial, instrumentation, powerline, and medical data acquisition card applications, reducing cost and speeding time to market, while taking up little space and being easy to use, at 1 MSPS True 16-bit precision.

PLC application example

Figure 1 shows a simplified signal chain for using PLCs in industrial automation and process control systems. PLCs typically include analog and digital input/output (I/O) modules, central processing units (CPUs), and power management circuits.

In industrial applications, analog input modules capture and monitor remote sensor signals in harsh environments, such as environments with extreme temperatures and humidity, vibration, and explosive chemicals. Typical signals include single-ended voltage or differential voltages with 5 V, 10 V, ±5 V, and ±10 V full-scale ranges, or loop currents from 0 mA to 20 mA, 4 mA to 20 mA, ±20 mA. When encountering long cables with severe electromagnetic interference (EMI), current loops are often used because they themselves have good immunity.

Analog output modules typically control actuators such as relays, solenoids, and valves to form a complete automated control system. They typically provide an output voltage with a full-scale range of 5 V, 10 V, ±5 V, and ±10 V, and a loop current output of 4 mA to 20 mA.

Typical analog I/O modules include 2, 4, 8, or 16 channels. To meet stringent industry standards, these modules need to provide overvoltage, overcurrent, and EMI surge protection. Most PLCs include digital isolation between the ADC and the CPU, and between the CPU and the DAC. High-end PLCs may also have channel-to-channel isolation as defined by the International Electrotechnical Commission (IEC) standards. Many I/O modules can individually program software for each channel's single-ended or differential input range, bandwidth, and throughput.

In modern PLCs, the CPU automatically performs multiple control tasks and makes intelligent decisions using real-time information access. The CPU may contain advanced software and algorithms as well as web connections for error verification diagnostics and fault detection. Common communication interfaces include RS-232, RS-485, Industrial Ethernet, SPI and UART.

Figure 1. Typical PLC signal chain

Figure 1. Typical PLC signal chain

Discrete data acquisition system solution

Industrial designers can use discrete high-performance components to build analog modules for PLCs or similar data acquisition systems, as shown in Figure 2. Key design considerations include input signal configuration, overall system speed, accuracy, and accuracy. The signal chain shown here uses the ADG1208/ADG1209 low-leakage multiplexer, the AD8251 fast-set programmable gain instrumentation amplifier (PGIA), the AD8475 high-speed funnel amplifier, the AD7982 differential input 18-bit PulSAR® ADC, and the ADR4550 ultra-low noise reference. power source. This solution offers four different gain ranges, but with a maximum input signal of ±10 V, designers are bound to worry about multiplexer switching and settling times, as well as other analog signal conditioning issues. In addition, achieving true 16-bit performance at 1 MSPS rate can be a serious challenge, even when using these high-performance devices.

The AD7982 has a full-scale step 290 ns transient response performance. Therefore, to perform the conversion at 1 MSPS rate while guaranteeing specified performance, the PGIA and funnel amplifier must be established in 710 ns. However, the AD8251 has a settling time of 785ns for a 10V step to 16-bit conversion accuracy (0.001%), so the guaranteed maximum throughput of the signal chain will be less than 1 MSPS.

Figure 2. Analog input signal chain using discrete components

Figure 2. Analog input signal chain using discrete components

Integrated solution simplifies data acquisition system design

The 16-bit 1 MSPS ADAS3022 data acquisition system IC is manufactured using proprietary high-voltage industrial process technology iCMOS® with integrated 8-channel, low-leakage multiplexer; high-impedance PGIA (with high common-mode rejection); high-precision, low-drift 4.096 V reference Voltage source and buffer; 16-bit successive approximation ADC. See Figure 3.

Figure 3. Functional Block Diagram of the ADAS3022

Figure 3. Functional Block Diagram of the ADAS3022

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AC contactor:

pe

KNC1-09

KNC1-12

KNC1-18

KNC1-25

KNC1-32

KNC1-40

KNC1-50

KNC1-65

KNC1-80

KNC1-95

Pick-up voltage
50/60Hz(V)

(0.85~
1.1)Us

(0.85~
1.1) Us

(0.85~
1.1)Us

(0.85~
1.1)Us

(0.85~
1.1)Us

(0.85~
1.1)Us

(0.85~
1.1)Us

(0.85
~1.1)Us

(0.85~
1.1)Us

(0.85~
1.1)Us

Release voltage
50/60Hz(v)

(0.2~
0.75)Us

(0.2~
0.75)Us

(0.2~
0.75)Us

(0.2~
0.75)Us

(0.2~
0.75)Us

(0.2~
0.75)Us

(0.2~
0.75)Us

(0.2~
0.75)Us

(0.2~
0.75)Us

(0.2~
0.75)Us

Coil power

50Hz

60Hz
 

Pick-up(VA)

70

70

110

110

110

200

200

200

200

200

Holding(VA)

8

8

11

11

11

20

20

20

20

20

Pick-up(VA)

80

80

115

115

115

200

200

200

200

200

Holding(VA)

8

8

11

11

11

20

20

20

20

20

Power
consumption
(W)

1.8~2.7

1.8~2.7

3~4

3~4

3~4

6~10

6~10

6~10

6~10

6~


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