Making your remote monitoring work

When choosing a remote monitoring system for your manufacturing facility, you have three options: PC clients, Web interfaces, and handheld devices, such as PDAs.

Each option has advantages and disadvantages, but choosing a development platform that you can use to build all three will give you the most flexibility.

Furthermore, choosing a monitoring option that easily incorporates the I/O and data processing in the various manufacturing processes and subprocesses speeds development time and eases maintenance.

One common way to remotely monitor processes is with a PC client. These provide the most depth of any remote interface. They can access historical databases, show data trends and views of alarms and events, and provide an overview of the complete system. A good client software package should offer both I/O and data integration and functionality for data processing. For I/O connectivity, an OPC client and server integrated into the system will allow the integration of most devices.

Another useful feature here is a historical database, which is helpful for data processing. National Instruments' LabView system has a database with interactive tools to allow browsing for data on networked clients, which users can then analyse and use for reports.

Another option for remotely monitoring process data is a Web page. Some industrial controllers run an embedded Web server. With this technology, you can open a standard Web browser, type in the IP address of the controller, and then view and control the process. This is especially useful if you need to change a setpoint or monitor a controller off site. However, Web browsers are not a very suitable option for performing analysis and sharing reports. You must export the data from the HTML file to a more appropriate analysis and report generation program.

A third way to remotely monitor process data is using a handheld device or PDA. These offer the most portable monitoring solution, allowing users to acquire data at a test fixture or to spot check a process. In addition to data acquisition, the PDA can perform some limited analysis.

Connectivity to I/O is achieved using standard wireless protocols or through serial links. However, handhelds are limited in what they can do because extensive processing is very power consuming, so they should be complemented with a desktop application.

Platform games

Once you are familiar with the different options for remotely monitoring data, you must examine each process and subprocess. Many independent subprocesses occur around a factory. When choosing a development platform for a subprocess consider one that you can easily integrate into the main process. This has many benefits for monitoring the system. Single operator interfaces can provide more information on the entire process because data can be easily shared between subprocesses. One example of an independent subprocess is a vision inspection system.

Mirelec Ingenieria, of Spain, used National Instruments products to build a vision inspection system that examines ice cream cones for defects. They chose their system because they could easily integrate the data acquisition with the vision inspection hardware, and the software could perform the analysis they needed.The system looks for three types of defects: irregularities around the crown; holes or stains on the surface; and two or more cones stuck inside each other.

A proximity sensor triggers two cameras to acquire the image of the cones. Software performs edge detection and statistical analysis routines to look for defects. If the system detects a defect, the data acquisition board activates the electrovalve, which opens and closes the reject doors.

Selecting a development platform with integrated data acquisition and vision was key for this application. The application was much easier to develop because it was developed completely in a single environment, LabVIEW. The acquisition, analysis, and monitoring systems were all built with one set of software tools. This also speeded up the debugging and maintenance.

Processing points

When thinking about data processing needs for your system, you should consider your monitoring needs. You can analyse data at several different points in the system. Commonly, it is done offline on the client or other desktop machine. This is useful because these machines are not being dedicated to controlling the process, and they traditionally have more computing power. However, the analysis results are delayed. In some cases, you may need to analyse the data while the process runs. One solution is to perform the analysis on the controller.

When selecting a controller, you have two top options - PLCs or PCs. Traditionally, PLCs offered the most reliability and PCs the most flexibility. Now a new class of controller, the PAC or Programmable Automation Controller, combines reliability and flexibility into one package.

When deciding how you are going to use remote monitoring, it is important to consider the strengths of each option. Traditional PC clients offer the most connectivity and analytical power, yet are confined to an operator station. Web clients offer the capability to monitor or control the process from anywhere on the network; however, they provide an individual view and are not meant for storing or sharing data. Handhelds offer the most portability, but again are not meant for data storage or sharing.

Thinking carefully about your I/O connectivity and data processing needs can help you make the best decision about your remote monitoring system.

Katie Shiels is product manager for LabView at National Instruments