Tag Archive: real time

Totalizing with dataTaker DT8x Data Loggers

Utilizing dataTaker Intelligent Universal Input Dataloggers

CHESTERLAND OH—December 13, 2011

Systems integrators often receive requests for help with datalogging applications that require totalizing to get volume, event counts or the total energy produced or consumed. Using the internal channel variables and calculation capabilities of the dataTaker DT8x series of intelligent dataloggers, it is quite easy to capture cumulative totals as well as to total over a particular period of time such as a day, week or month. There are 2 types of signals that can be totalized: analog signals like a 4-20mA current loop from a device like a flow meter, and digital signals from a switch or pulse output meter. The technique to totalize each is slightly different.

When totalizing analog signals, a very common application involves reading a flow meter which provides a 4-20 mA output to display the instantaneous flow rate and then integrating this flow rate to get volume. dataTaker data loggers provide 2 built-in functions to automatically integrate measured values. The IB Data Manipulation function provides a simple 2 point integration by taking the average value calculated from the current sample and the previous sample and dividing by the time difference between the 2 samples. The INT Statistical function will sample the input at a rate determined by the statistical schedule and perform an integration using a trapezoidal approximation.

The main difference between these 2 techniques is how often the input is sampled to perform the integration. The IB function will only sample based on the main schedule rate, whereas the INT function samples at the statistical schedule rate. For example, if the main schedule was set for a 1-minute sample interval and the statistical schedule was set for a 10 second interval, the IB function would sample the input once every minute and integrate using just these 2 points while the INT function would sample every 10 seconds and return the sum of these 6 smaller integrations. While the INT function requires more resources and may not be appropriate for an application that requires low power, the advantage is obvious–it provides much better accuracy for situations where the flow could change rapidly–for example in a process machine that may be switching the flow on and off during different parts of the process cycle.

In either case, the function only provides the total over the sample interval, so it is necessary to use an internal variable to accumulate the total over a longer period of time. Using the += function provides a convenient way to do this. Simply pick a CV to use for the total, select the Assign to channel variable and then CV = CV + value, and you will now have a variable that contains the total value.

It’s also important to keep in mind the scaling with respect to these functions. Both functions work in units of seconds, so it may be necessary to adjust the scaling to get the returned value in the desired units. For example, if the desired units for the flow rate are in gallons per minute (GPM), then the value returned by either of the integration functions must be divided by 60 to convert from seconds to minutes to get the correct units.

In some cases all that is required is to accumulate the total since the start of the program, while other applications may require a daily, weekly or monthly total. In these cases, another schedule within the logger (in conjunction with an alarm if necessary) can be used to reset the total. For example, if only a daily total was required, a second schedule could be created to run once a day and within this schedule the CV containing the accumulated total could be set to 0.

For other reset intervals, the data logger also provides an internal channel for the day of the week (4ST) along with system variables for the day of the month (20SV) and day of the year (21SV). These can be used in an alarm statement to reset the channel variables containing the totalized data via the Action Command. Finally, it is also possible to use a manually triggered schedule to reset the counters. In this instance the schedule (triggered by an external switch or pushbutton) can contain the commands to reset the variables containing the accumulated total to zero.

Totalizing a device with a digital pulse signal output is easier than a sensor with an analog output. The dataTaker datalogger has 2 sets of counter inputs that can be used to count pulses. Any of the digital inputs 1D-8D (1D-4D for DT82 loggers) can be used as a low speed counter to measure pulses up to 25 hZ. Be aware, however, that these counters are not active if the logger is asleep, so they are not suitable for applications that require the lowest power consumption when the logger is allowed to sleep between samples.

If it is necessary to measure higher speed pulses, the loggers also provide 4 high speed counter inputs that can measure pulse frequencies up to 10 kHz. These counters can automatically accumulate the number of pulses, so that with the appropriate scaling they can provide a direct output of totalized flow. However, the counters are 32 bits wide, so it is possible for them to overflow and wrap back to zero. These counters also have a resetting mode whereby they are reset to zero after each time they are read. It is possible to combine the resetting mode with a channel variable that uses the += function to provides an accumulating counter in software. In this case, the counter is read, added to the totalized count that is contained in a variable, and then reset to zero to start the next count interval. Just like the analog counters, the digital counters can be reset by a schedule with an alarm command if necessary to periodically reset the total.

Check out the dataTaker product overview page here.

For further information on the dataTaker DT8X series of intelligent universal data loggers, other dataloggers in the highly successful dataTaker line, 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.

Contact Information:
CAS DataLoggers, Inc.
12628 Chillicothe Road
Chesterland, Ohio 44026
(440) 729-2570
(800) 956-4437
sales@dataloggerinc.com
http://www.dataloggerinc.com

How To Choose the Ideal Data Logger

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.

Contact Information:
CAS DataLoggers, Inc.
12628 Chillicothe Road
Chesterland, Ohio 44026
(440) 729-2570
(800) 956-4437
sales@dataloggerinc.com
http://www.dataloggerinc.com