USB data acquisition card, labjack u12 used in industrial control

Abstract: USB data acquisition controller is used in PC-based systems. Because of its ease of use and high price ratio, it has occupied a majority of the original data acquisition control card market, not only has it been widely used in OEM equipment, but also has replaced the traditional PLC system in many occasions and is applied to industrial control. This document uses labjack u12 as an example to describe how to use a USB data acquisition controller in industrial process control.

Other labjack Data Acquisition cards are also applicable:

Labjack u12 data acquisition card

1. Introduction to USB data acquisition controller
   Labjack u12 is a multi-function USB data acquisition controller, which has the highest cost performance among similar products. It has 8 analog input channels, 2 analog output channels, and 20 programmable digital input and output channels. It has been widely used in experimental/experimental equipment, automatic testing equipment, and other PC-based systems. Is an ideal OEM part.

It is also increasingly used in industrial process control. The PC-based system consists of all the inherent advantages of PC-based systems, such as short system development cycle, easy system change, bright user interface, and easy operation, process Monitoring, alarms, records, and printing can be performed, and various control algorithms that cannot be implemented by PLC can be implemented by the computing power of computers for Complex Process Control and other advantages. With the help of our company's configuration of other peripheral devices and configuration software, the system development is simpler and faster, and its application is more extensive.

This article will introduce the control system consisting of labjack u12 and the aspects to be paid attention to. Based on this, it will introduce how to expand the scale of the system and the required modules, next, we will introduce how to use redundancy technology to improve the reliability of the system.

2. System Composition
   2.1 single labjack u12 System
   Some simple control systems only need one labjack u12. Its system composition 1 is shown in. U12
   Powered by USB, all input and output ports can be connected to and connected to u12 and cb25. Such a system is very simple and used by most OEM devices.
   

Figure 1: single labjack u12 System

2.2 System Expansion
For most industrial control systems, the input and output ports of a single labjack u12 are insufficient. Therefore, the system needs to be expanded. Using a USB hub can easily extend the entire system to a very large system. A computer can connect up to 80 labjack u12 instances, and a USB hub can be horizontally connected. The extended topology of the system is shown in figure 2. If the USB hub is 1-out 4, the extended system can connect 16 labjack u12 instances. If it is an out-of-8 hub, the extended system will have 64 labjack u12.

Figure 2: system extended Topology

2.3 Digital Port Drive Module
In industrial control systems, digital outputs are often used to control relays or Intermediate Relays, while intermediate relays are used to control contactor control. The digital output drive capability of labjack u12 is limited. It can only drive the TTL door circuit or LED, and cannot directly drive the relay coil; the output level is 5 V, which is incompatible with the commonly used 24 V in industrial control. Therefore, the digital output needs to be connected to a drive module od25.

The connection between od25 and labjack u12 is mainly through a db25 line. It provides drivers for all the digital interfaces of labjack u12. The driving voltage can reach 50 V, the driving current can reach 500 mA, and multiple relays can be directly driven at the same time (if necessary ). Therefore, od25 is generally essential in industrial control systems.

Od25 also provides connections between other modules and labjack u12. Generally, its other db25 plug-in is connected to cb25 or oi25 as the wiring board for digital input. When the number input is high, the corresponding digit led on od25 will light up, and this led is very useful in system debugging and program debugging. Use od25 System 3.

Figure 3: system diagram using the digital drive module

2.4 cb25 and oi25 modules
Cb25 is just an wiring board that provides the D0-D15 of digital ports, digital ports input and output direction is determined by the software, so if the digital input ports do not need to be isolated, use cb25.

Oi25 is a photoelectric isolation module for digital input ports. The Application of photoelectric isolation is complex. How to isolate it depends on the signal source (for example, whether it is dangerous to be struck by lightning or whether it comes from different electrical systems), the nature of the signal (AC or DC), and the requirements of the system in this regard. In addition, it must be pointed out that if isolation is adopted, the entire system must be considered, rather than the isolation of digital ports, such as 485 Communication Ports and analog signals. There are often some misunderstandings in this regard, but we will not detail them here. The following describes only system applications that do not require isolation. However, this does not mean that the system composed of labjack has any problems or inconvenience in isolation. In fact, like any other system, the cost of the system will increase significantly if the system needs to be isolated by adding isolation modules.
2.5 use of other devices
In industrial control systems, there are often other equipment, such as inverters and other instruments. Most of their connections to computers use interfaces 485, which are independent of labjack u12. The PC-based system is structured as a single processor, that is, all data processing and control depend on the PC processor, therefore, the concept of DCS must be introduced in some aspects of image control, that is, local control adopts a separate instrument. The real-time control system is completed by the instrument or controller, while the PC only adjusts the parameter and control target value of the instrument at the macro level.

There is a counter on labjack u12, which can be used to detect frequency signals. If there are many frequency signals, you can use the frequency-voltage conversion circuit and output it to the analog input port. For the signal of rotary encoder, can use special instruments, can also use the company's DSS-FC2 module. This module uses the sound card processor to greatly reduce the main CPU burden on the PC, so the efficiency is high.
2.6 System Software
Labjack u12 provides a universal dynamic link library, so you can use any programming language. The Configuration Software daqfactory provided by the company should be the preferred software development platform, because the configuration package includes all the free labjack u12 drivers, you do not need to know how to program labjack u12 when using the configuration software. You only need to make some simple settings on the screen, and the development cycle will be greatly shortened. Www.pc17.com.cn more details

USB data acquisition card, labjack u12 used in industrial control