Before You Buy a Data Logger, Read This!
CHESTERLAND OH—October 10, 2011
Solutions providers field hundreds of calls and emails weekly addressing the same question: “Which of the data loggers you carry best fits my application?” Whether you are an engineer working out the details of your latest project or a buyer filling a requisition, the number of available options when choosing your data logger can often be overwhelming. For this reason, the majority of calls begin with this simple question: “What are you looking to accomplish?” In fact, placing a call to a solutions provider is the quickest way to get the information you need to proceed.
When choosing a datalogger, consider your short- as well as long-term needs. Are you looking to solve a specific short-term problem or are you are looking for a multipurpose tool to handle current requirements as well as being flexible enough to accommodate future project needs? A popular example of the latter is the dataTaker family of data loggers which have been designed to record almost any physical value and which can easily be expanded with more channels when the need arises. In general, an experienced provider will ask specific questions to help you determine which products are the most suitable including how many inputs are required and what type; how often you need to take a reading; how much data needs to stored; how the data logger will be used; how you’ll communicate with the device; and any other requirements the application might have.
Your first consideration is to determine the number of inputs you plan on logging. Since data loggers are available in configurations capable of handling anywhere from one to literally hundreds of inputs, knowing what you need now and possibly in the future will have a significant impact on your choice. The Grant SQ2020 WiFi wireless portable data loggers are available in 8 to 16 channel models–watch this video. Meanwhile the dataTaker DT80 series of dataloggers, for example, can be configured to monitor anywhere from a single sensor to over 300 inputs. Do you need a logger with external sensors or can you use a logger with a built-in sensor like the TandD RTR-51 wireless temperature datalogger? This initial question-and-answer phase is the best time to engage a representative in online chat or a fast phone call.
Since dataloggers are designed for such a wide variety of applications, knowing the type of sensors or inputs you plan on using is critical. For instance, if you already have a thermocouple and you need to log temperature readings, the simple or inexpensive temperature data logger that caught your eye might not be suitable if it comes equipped with a dedicated RTD. If all you need is to record data from 4 individual 4-20mAmp current-loops, a simple 4-channel logger dedicated to process current loops might work fine. A single, 0-5 VDC? Again, a simple dedicated data logger might do the trick. On the other hand, if you are mixing inputs (current-loops, voltages, pulses, etc.) you’ll need a more flexible, sophisticated data logger.
A good solutions provider will be able to offer you a diverse selection of data loggers compatible with most types of signal inputs. While some of these loggers are dedicated to a certain input type, others are user-configurable for different types and infinite combinations of signal types. Many models of data loggers are available on the market for the following types of signal inputs: AC Voltage, Process Current, Bridge, Strain, Load, Pressure, Dew Point, Event (or State), Frequency, Level, Process Voltage/Current, PH, Relative Humidity, RTD, Shock, Acceleration, Sound, Temperature, Thermocouple, Pulse, Serial and more.
Another important consideration is how often you need to record a reading. Most data loggers can handle recording at rates up to about 1Hz (once per second). If you need a faster recording frequency, be aware that as the speed of the data logger increases, the price of the data logger does as well. Make sure that the recording rate you are specifying is appropriate–in the case of a K-Type thermocouple, for example, the sensor/sample may take several seconds to change temperature. Recording such a temperature with the data logger at 5Hz would provide redundant or useless data.
Depending on your application, you may need to only capture a few minutes’ worth of data or you may need to be able to store whole months of readings. You can determine the amount of data storage required by multiplying the number of channels by the sample rate and recording duration:
Total Number of Points = Number of Channels X Sample Rate X Recording Duration
Depending on the data logger, there may be a limit based on the total amount of internal memory, or the logger may offer the option of using external memory such as a USB memory stick to expand the available memory.
It also important to consider what is practical for the application and analysis. Many users initially state that they want to record multiple channels of data at hundreds of Hz. One problem with this is that this would quickly fill the available memory and necessitate more frequent downloads. Even worse, it becomes impractical to analyze all the data–with a high speed data logger sampling at 100 Hz, users can exceed the maximum number of rows in Excel in just over 10 minutes!
In this case you’ve got a handy guideline- if you’re looking for trends, use the statistical capabilities offered by certain data loggers to summarize the data over an interval. If you’re looking for anomalies, use the logger’s triggering features to just capture a window around the event.
Naturally, there are data loggers that are designed for fixed installation and others that are intended for more portable applications. When considering how the logger will be used, keep these key issues in mind: how will it be powered–by battery, AC adapter, or solar panel? Will the logger be used in a lab or does it need to be protected from moisture and dirt? Does it need to be completely self-contained so that it can be used in the field? Checking the IP rating of these devices will provide you with a good idea of the punishment they can take, and some loggers such as the Grant Squirrels can endure full exposure to the elements!
Ultimately you have to retrieve the data from the data recorder somehow, so do you plan to bring the logger to the computer to download data, or would you prefer to handle it remotely? Communication with the data logger for set-up of monitoring and downloading data can be done in many different ways, including serial or RS-232 interface, USB or Ethernet interface, wireless capability including Wi-Fi and proprietary RF links, analog telephone (PSTN) modem, cellular, CDMA or GPRS/GSM modem, and satellite modem. If your application needs a remote solution, for example, check out the wide range of wireless solutions provided by Accsense monitoring and alarming systems here.
In addition to basic data collection, does your application require other features such as alarms? Does the data logger have to perform real-time calculations on the measured data? Do you need a local display or output signals? These are the details you’ll need to request to your provider to ensure your logger is a perfect fit for your specific application.
Given the amazing range of data logging products on the market, and before you make your choice of manufacturer and model, make sure you speak with a trusted solutions provider to find out how to get the most suitable device for your specific application at the most affordable price. A good provider can offer you experienced help over the phone as well as live chat support and a detailed online store listing specifications. Make sure your provider also offers critical value-added services such as customization, configuration, and more.
For further information on the Grant Squirrel 20xx family of data loggers, Accsense wireless monitoring solutions, or to find the ideal solution for your application-specific needs, contact a CAS Data Logger Applications Specialist at (800) 956-4437 or visit the website at www.DataLoggerInc.com.
CAS DataLoggers, Inc.
12628 Chillicothe Road
Chesterland, Ohio 44026