How do I choose a digital recorder?

A reader considers using web-based recorders to help with remote diagnoses, but will he have to give up any functionality with web-based vs. today's digitals? And what about software considerations?

QUESTION:

We're making a long overdue change from mechanical analog chart recorders to digital recorders for our heat-treating machinery. We've been told also to consider web-based recorders that might help us with remote diagnoses. Do I give up any functionality with web-based vs. today's digitals? What about software considerations?

--From June 2006 Control Design

ANSWERS:

A Few Digital Choices
When choosing a new recorder to replace the traditional mechanical analog recorders, there are a number of factors to consider. Today’s digital recorders fall into two major categories--digital chart recorders that still use charts and consumables, and electronic paperless recorders. Both are capable of replacing the traditional mechanical analog recorders, but a key factor in this decision should be based on how the data is to be used and distributed. Digital chart recorders provided a good graphical presentation of what happened in the process, but they make for a time-consuming process to convert the data from the paper chart to a form that allows use of advanced statistical analysis tools. Paper charts also made it difficult to let others know how well the process performed because they cannot easily be duplicated or transmitted to other locations. 

 Generally, digital chart recorders have configuration software available to aid in the set up of the recorders; beyond that they depend on higher-level software packages to support real-time data acquisition. Paperless recorders also have configuration software packages and they come with software to aid in data analysis. Many include additional functionality to aid in doing real time or scheduled FTP data downloads. 

 Paperless recorders such as our X-Series recorders incorporate graphic displays to show trends, bar graphs, digital values or combinations of these basic displays, or provide the ability to have customized displays; they store the data electronic for local replay and enable data acquisition over a network. Having the data in an electronic format allows for faster, more comprehensive analysis of the data. It eliminates questions of data resolution, the need for interpolation of trace values from a chart and the associated errors of transferring the data to a spreadsheet for further analysis.

In addition to improvements in data reliability, the user also benefits from reduced maintenance costs from elimination of many of the mechanical parts such as chart drives and pen mechanism associated with conventional paper recorders. Paperless recorders typically provide a higher degree of connectivity to a network than digital paper chart recorders; many support Ethernet connectivity allowing users to connect these to a LAN or the web for remote data access. Finally, the elimination of consumables such as the charts, pens and ink wheels normally used by paper recorders provides additional savings. They allow for better decision-making as a direct result of having quick access to reliable data that is easy to work with and provides a lower cost throughout the overall process of delivering quality goods to the customer.

Douglas Bradway, senior product manager, data acquisition, Honeywell Process Solutions, Phoenix, Ariz.


Don’t Go Web-Only

Monitoring and profiling of heat treatment equipment is an excellent application for a digital recorder. Even the simplest of today's multichannel recorders provide excellent accuracy and repeatability not possible with a pen and paper.

Most recorders these days can handle a variety of inputs, from thermocouples to DCV and DCmA, with just a few switch throws and software radio buttons. The majority of digital recorders are very capable of monitoring and recording data with greater accuracy and additional functionality, which results in higher quality parts and lower costs.

A subtle but fine difference is that web-based equipment relies on the Internet to function. If the connection is lost, the system is down and recording is not possible. A web-enabled device such as our IntelliLogger is a standalone recorder capable of communication over the Internet as well.The IntelliLogger is capable of storing all recorded data to onboard internal memory and then when initiated, the data file can be e-mailed or sent to multiple sites for use and/or backup. Alarms, SMS, and ftp capabilities expand the functionality of any web-enabled recorder, providing autonomous data download, storage, and alarming. The device also is a web server, serving up standard and custom web pages with real-time data, allowing interested parties to perform in-process monitoring. 

 Regarding software, look for something that is easy to use and does not require writing lines of code. A graphical environment for communications, programming and even web page creation is best.

onnecting the dots is about the same complexity but allows for intelligent and conditional programming scenarios if desired.

Bottom line, the only reason to keep a analog chart recorder is legacy. The new systems offer more flexibility, alarming capabilities and communications options then ever before.

Mark Albert, Logic Beach, La Mesa, Calif.


Check List for Choosing

This is a common question that challenges lot of the plant personnel in today. Typically the problems that users run into with paper recorders relate to running out paper, pens running dry, problems with mechanical assemblies etc. By carefully selecting a digital or paperless recorder the plant user can overcome lot of these problems. 

Some things to consider: 

Paperless recorders generally are available as a standard replacement for paper recorders with standard cutout dimensions for the panel. This will save a lot of headache later. 

It always is a good idea to get a recorder with a broad-ranging power supply 115-230 VAC, 50/60 Hz. A side question ask whether the recorder has supply voltage for loop power of 24 V with a max 32 VDC, and max current rating of 250 mA. This allows for field instruments to be powered directly from the unit.
 How many inputs are hooked up to existing recorders? Recorders with three to six inputs are commonly available, and it always is a good idea to see if they'll accept universal inputs (mV, RTD, thermocouple, 4-20 mA). This allows for easier implementation. 

Is totalizer functionality required? If yes, it'll be a good idea to get the totalizer function to integrate the analog inputs. 

Does the recorder have an internal SRAM memory? Can external CompactFlash cards be used in conjunction with the recorder without the need for any additional hardware? 

Is there a software available from the manufacturer that allows for configuration as well transfer of data from the recorder? It's also a good idea to evaluate the license fees and or update fees that might be applicable for the software upfront. Is there a software available to allow data transfer to a HMI software? All data stored on the recorder should be in a secure format that does not allow any tampering. 

Does the recorder have the capability to give the user choice of programming from either software or using a keypad on the unit with user friendly menu? 

Does the recorder have an embedded web server? It will simplify tracking data remotely from anywhere in the world with help of a web browser. 

Does the recorder have capability for RS232/RS485, USB or Ethernet interface? This will help in communicating data with other devices. 

Does the recorder have an option for relays that can be used for set points? 

Does the recorder have mechanical lock capability to provide reliable data archiving and prevent unauthorized access?

Ravi Jethra, product manager, Endress+Hauser, Greenwood, Ind.


More, More, More
Visit the ControlDesign.com archive for more background information on digital recorders. We recommend:

Data Collection Need Defines Recorder Selection. Field Editor Kevin Russelburg reported in this installment of SpecMate that for machine builders, even a basic videographic recorder offers several advantages over chart recorders. Read all about it at ControlDesign.com/articles/2005/306.html.

Also, Digital Editor Rick Pedraza just completed a Product Round-Up on data loggers, recorders and systems. Review all the products at ControlDesign.com/articles/2006/106.html.


  November's Problem

We Need Machine Advice
As a custom machine builder, we have to include machine vision once in a while as part of the overall control scheme. We’re considering the pros and cons of just buying a turn-key, all-in-one vision sensor package vs. something more versatile and powerful, even if it means doing some of the component integration ourselves to have the in-house expertise. It’s the software that scares us about that. I’d like to hear some advice about both approaches.

Send us your comments, suggestions, or solutions for this problem. We’ll include it in the November 2006 issue, and post it on ControlDesign.com. Send visuals if you’d like—a sketch is fine. E-mail us at CDTheAnswer@putman.net. Please include your company, location and title in the response.
Have a problem you’d like to pose to the readers? Send it along, too.

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