DATAQ Instruments Application Notes and News

Same Great Content with a New Look

image_pdfimage_print

We are proud to announce a top-to-bottom redesign of www.dataq.com. This effort draws upon your comments over the years to yield a new look and feel while providing easier access to information.

DATAQ Instruments, Inc. New Home Page

DATAQ Instruments, Inc. New Home Page

Among other improvements you’ll find a new Products menu that puts you only a few mouse hovers away from a range of product solutions for most applications. We’ve laced the website with product filter pages that allow you to easily determine product options for specific requirements. And all product pages have a clean, easy-to-use design that describe the product, its price, available options, and similar alternative solutions.

Please take some time to explore the new website that you helped to deign, and feel free to let us know your thoughts in the comment section.

 

WinDaq/XL Real-time Bridging Software

image_pdfimage_print

WinDaq/XL is real-time bridging software that allows users to stream data from WinDaq data acquisition software or the WinDaq Waveform Browser, into a Microsoft Excel spreadsheet. Once there, users can take full advantage of Excels exceptional ability to perform calculations and chart data.

Since it’s initial release several years ago, features have been added to WinDaq/XL, and the data storage capacity of Microsoft Excel has expanded from 65,536 rows, to well over a million.

A ‘High Speed’ option in WinDaq/XL now allows data to be buffered for high speed data acquisition, and the time/date stamp is fully customizable.

WinDaq/XL Real-time Bridging Software

See our multimedia presentation demonstrating the power of the WinDaq/XL add-on!

 

Additional Reading:

WinDaq Data Acquisition Software-to-Excel Real Time Link

Getting Started With WinDaq/XL

WiFi Range Considerations

image_pdfimage_print

We carry several WiFi products and we’re often asked about their range. In other words, how far from the WiFi router can the data loggers be located? Unfortunately, this is like asking us to forecast the weather next Sunday. There are simply too many variables for us to predict how well any WiFi product will operate in all but the most clear cut cases. Beyond the distance between the data logger and the WiFi router, WiFi range is affected by the number of walls and floors that separate them, their construction, ambient levels of electromagnetic activity, electrical wiring density, and more.

None of this helps you arrive at an answer for the range question, but here are some ideas that may.

WiFi Range Audit

Why not discover the answer to the WiFi range question empirically? Given the proliferation of  WiFi-enabled portable devices (most notably cell phones and tablet computers), try syncing such a device to your WiFi network, place it where you want to locate the WiFi data logger, and see how well it performs. Try downloading a large file to get a feel for the fidelity of the WiFi signal in your area of interest. If the download goes well, you have every reason to believe that a WiFi data logger will work equally well.

The Unintentional WiFi Faraday Cage

A Faraday cage is a metallic enclosure that impedes or inhibits electromagnetic energy. Radio devices placed inside such a cage occupy an RF dead zone. Unfortunately, many environments  where customers need to make measurements are unintentional Faraday cages. I’m thinking of ovens, refrigerators, and  freezers that are usually if not always constructed with a grounded metallic shell. Placing a WiFi product inside such an area may isolate it from the outside RF world. Again, use the WiFi Range audit suggestion above to predict performance in this situation. Start a large download, and then place the device inside the environment and close the door.

External WiFi Data Loggers

When an environment that you’d like to measure presents a Faraday cage-like dilemma, consider a probe-type data logger where the probe is placed in the monitored environment while the WiFi data logger remains outside. Many ovens, refrigerators, and freezers provide an instrument port for such a purpose, so you won’t have to drill holes in most cases.

Further reading:

EL-WiFi Series Data Loggers

TemperatureAlert Data Loggers

 

 

Why You Need Channel-to-channel Isolation

image_pdfimage_print

It’s difficult to temper excitement about DATAQ Instruments’ model DI-245 data acquisition system. Beyond thermocouple-based measurements and a superb voltage measurement range, there’s the instrument’s incredible isolation specification. We’ve given you a multimedia presentation and a related post that describes it (see here and here), but this post focuses on an often-overlooked nuance of isolated instruments.

Channel-to-channel Isolation

Trouble without channel-to-channel isolation.

DI-245 high common mode voltage application (click to enlarge.)

Many instruments offer input-to-output isolation and tout that as a great feature. Some isolation is better than none, but it’s important to understand exactly what you get with an instrument that offers only input-to-output isolation: All channels share a common ground that is isolated from power. There are no consequences to this if you connect only one channel to a multi-channel instrument. That single channel’s ground reference is free to float to any value within the isolation spec of the instrument without damage. However, connect a second channel at the same time and you could be headed for major problems.

A nearby graphic reproduces the test setup we used in our multimedia presentation where we deployed the DI-245 in a high common mode voltage situation. Can you imagine what would have occurred if the DI-245 supported only input-to-output and no channel-to-channel isolation? Right…instant fireworks. If it isn’t clear why, look closely at the relationship between channels one and two. Channel one has been driven off ground by a 340-V peak-to-peak signal (ordinary US line voltage), while channel two is grounded. If the DI-245 lacked channel-to-channel isolation, meaning all input channels share the same ground, connecting channel two in the manner shown shorts line voltage to ground. Ouch! Fortunately, we anticipated this problem and designed the DI-245 with both input-to-output and channel-to-channel isolation.

So, why would any manufacturer design a product with only input-to-output isolation (and there are many who do?) It simply costs less to provide only input-to-output isolation, which translates into a lower selling price while still allowing the company to advertise the product as having isolation. It’s a smokescreen laid in front of a bear trap for customers whose budgets match their instrumentation experience. With the DI-245 you can have it both ways: World-class isolation at a budget-friendly price.

 Additional Reading:

DI-245 mV, V, and Thermocouple Data Acquisition System

How To Calculate Common Mode Rejection Ratio

image_pdfimage_print

Common Mode Rejection Ratio Defined

Common mode rejection ratio doesn’t seem at all common. In fact, it sounds rather fancy and complicated. But it’s actually a simple concept. Recall that a common mode voltage is one that occurs simultaneously and in phase on both inputs of a differential amplifier. For a dramatic demonstration of this, please watch the video you’ll find at this link. Channel one’s applied signal in the video has two components:

  • A common mode voltage equal to 340-V peak-to-peak (standard US ac line voltage)
  • A normal mode voltage equal to the thermocouple signal.
Common mode and normal mode voltages

The relationship of common mode, normal mode, and output voltages when applied to a differential amplifier (click to enlarge.)

The nearby graphic helps to reinforce what’s actually going on in the demonstration. Line A in blue is a composite of the applied normal mode (thermocouple) and common mode (line voltage) signals that we applied to the (+) input of the DI-245’s channel 1. You can see that it doesn’t have a consistent amplitude, since it’s a sum of both the signal of interest (thermocouple) and the signal we’d like to reject (line voltage.) Line B in red is pure common mode signal without a normal mode component that’s applied to channel 1’s (-) input. You can see by studying these plots that the common mode component is applied simultaneously and in phase with both amplifier inputs. That prerequisite being met, the differential amplifier can do its job to produce an output that’s the difference between the signals applied to its inputs. The result is shown in green as line C. Of course, the relative signal amplitudes depicted in the plot are way out of proportion for clarity and to avoid complicating the issue with logarithmic scales. The common mode signal is hundreds of volts in the demonstration while the normal model signal is milli-volts with only micro-volt changes.

 Common Mode Rejection Ratio Calculation

Now that you understand what signal components are involved and how they relate, it’s time to actually calculate a measure of the amplifier’s ability to reject common mode signals and pass the normal mode signal of interest. The term common mode rejection ratio defines this measure and it’s the ratio of output-to-input signal magnitude. Turning back to the demonstration, we applied a 340-V peak-to-peak common mode signal. Since it’s ac in the shape of a sine wave at 60 Hz we should convert it to its dc equivalent for calculation purposes and use the value 120 Vrms. From the video the narrator noted that the signal on channel one moved the equivalent of about 9 micro-volts with the common mode signal applied. This implies a common mode rejection ratio value of: The above means that for every volt of common mode voltage we apply to a DI-245 input channel, the output will change by only 75 nV. Not bad for such an inexpensive solution as the DI-245! However, it’s kind of clumsy to refer to common mode rejection using scientific notation, so we commonly convert it into a logarithmic value in decibels (dB): equation2 So, in this demonstration the DI-245 may be described as providing about -142 dB of common mode rejection, meaning that the common mode voltage was reduced by 142 dB.

 A Word of Caution

Before you apply the demonstration and calculations referenced in this post, be sure that your instrument will tolerate a common mode line voltage. Most won’t and those that fail will do so spectacularly.

More reading:

Model DI-245 Thermocouple, Voltage, Millivolt Data Acquisition System

A Graphic Common Mode Voltage Demonstration

The Ability of the DI-245 to Reject Common Mode Voltage

image_pdfimage_print

The ability of the DI-245 to reject common mode voltage is unmatched in the $75 per channel price range.

To demonstrate the ability of the DI-245 to reject common mode (error) voltage, we connected K-type thermocouples to channels 1 and 2. With the thermocouple on channel 2 grounded, we then connected line voltage directly to the thermocouple on channel 1. This allowed us to demonstrate not only the common mode rejection, but also the channel-to-channel crosstalk rejection of the DI-245.

The ability of the DI-245 to reject common mode voltage As the following video illustrates, the results were impressive, to say the least!

Additional Reading:

How to Eliminate Noise in Data Logging and Data Acquisition Measurements Introducing the DI-245 Thermocouple and Voltage Data Acquisition System

EL-WIFI-Alert Alarm Indicator

image_pdfimage_print

The stand-alone EL-WIFI-Alert alarm indicator is an add-on for EL-WIFI series temperature and humidity data loggers. The EL-WIFI-Alert produces an audible and visual alert when an alarm level on one of your EL-WIFI temperature and humidity data loggers (installed on the same wireless network) is breached.

EL-WIFI-Alert alarm indicator

Multiple EL-WIFI-Alert units can be placed in remote locations, out of sight of the EL-WIFI loggers themselves and your PC, alerting users to alarms that might otherwise get overlooked. With 10 volume settings, 9 alarm sounds and bright, flashing LEDs, the EL-WIFI-Alert is a great compliment to the alerts already visible on your EL-WIFI logger and in the WIFI Sensor Software.

 

Additional Reading:

Configuring the All-new EL-WIFI-TH Using EasyLog WiFi Software

Cloud-based Device Management for EL-WIFI Data Loggers

4-20 mA Measurement Resolution

image_pdfimage_print

Don’t overlook a vital component that affects 4-20 mA measurement success: Measurement resolution.

Measurements from sensors that have a 4-20 mA output are very common. Customers always ask how to connect them to a data logger or data acquisition system, which we describe in detail here. However, they often overlook a vital measurement component that affects their 4-20 mA measurement success: Measurement resolution. This application note presents a table of popular product implementations from DATAQ Instruments and associated resolution values as a quick reference guide.

So, What’s 4-20 mA Measurement Resolution, Anyhow?

Good question! The term “measurement resolution” refers to the smallest change in an applied signal that an instrument can detect. Although this change can be described in terms of applied mA, it is more constructive to describe it in terms of measured units. For example, telling you a given instrument  has a measurement resolution of 80 µA is much less descriptive than saying that your measurement resolution is 0.50 psi. If the smallest measured change is too coarse, you need an instrument with higher resolution.

4-20 mA Measurement Resolution for Seletced Instruments

In the table that follows, just divide the full scale output of your 4-20 mA source by the indicated ADC Counts for a given Instrument to determine resolution in measured units. For example, a DI-145 Starter Kits applied to a 4-20 mA pressure sensor with a 0-1000 psi range provides 4.9 psi of resolution (1000 ÷ 204). A load cell with a full scale range of 100 lbs. applied to a DI-155 yields 0.020 lbs. of resolution (100 ÷ 5320.)

The table makes the following assumptions:

  1. You use either an external shunt resistor with a value of 250 Ohms, or an 8B32 or 8B42 process current amplifier (if the instrument supports them.)
  2. You have selected the optimum instrument voltage range for the measurement. For example, the 5-V range for the DI-155.
  3. Your 4-20 mA output is zero engineering units at 4 mA and full scale EU at 20 mA.
  4. The instrument supports only bipolar inputs.
Instrument ADC Counts Example (psi)* Comments
DI-145 204 4.9 External 250Ω shunt
DI-149 204 4.9 External 250Ω shunt
DI-155 ~5320 0.19 External 250Ω shunt
DI-245 6553 0.15 External 250Ω shunt
DI-710-xHx 6553 0.15 External 250Ω shunt
DI-710-xLx 3276 0.31 External 250Ω shunt
DI-718B 8192 0.12 DI-8B32 or -8B42 amplifier
DI-718Bx 8192 0.12 DI-8B32 or -8B42 amplifier
DI-788 8192 0.12 DI-8B32 or -8B42 amplifier
DI-720** 8192 0.12 DI-8B32 or -8B42 amplifier
DI-730** 8192 0.12 DI-8B32 or -8B42 amplifier

* Assumes a full scale measurement range of 1000 psi.

** With the DI-78B Backpack option.

 

How To Install Model DI-245 Under Windows XP

image_pdfimage_print

Since our new model DI-245 voltage, millivolt, and thermocouple data acquisition system was released after Microsoft very vocally discontinued support for Windows XP, the instrument is the first in a long while that does not natively support that operating system. We’ve since learned to our chagrin that Microsoft continues to provide XP support in some countries, creating a quandary: For the first time Windows operating system support is a function of your location on the planet. Sigh…

Customers who still use XP and who want to deploy the DI-245 on that platform can use this guide to do so. Installation is the same as for a contemporary OS, except that drivers need to be downloaded and installed separately. Here’s the procedure:

  1. Download DI-245 software from run.dataq.com.
  2. Install the software, which installs everything you need to use the DI-245 except drivers.
  3. When you connect the DI-245, your computer will complain that DI-245 drivers do not exist.
  4. Download a ZIP file containing drivers from this link, and unzip the contents to a folder in a known location on the target XP PC.
  5. Manually install the drivers from the Windows Device Manager. If you aren’t sure how this is done, this guide provides a step-by-step procedure. 
  6. Do not be alarmed by the dialog box stating that a driver may harm your PC. Simply click CONTINUE ANYWAY.
  7. PLEASE NOTE that you need to install two drivers, executing steps 5 & 6 twice, one for the USB port and another for the virtual COM port that the DI-245 hooks to communicate with the PC. The driver file that you downloaded contains both.

Your DI-245 is ready to use.

 

Introducing the DI-245 Voltage and Thermocouple Data Acquisition System

image_pdfimage_print

DATAQ Instruments is pleased to introduce the all-new DI-245 Voltage and Thermocouple data acquisition system. The DI-245 provides four analog inputs that can be individually configured to measure voltage or thermocouple data.  With 12 programmable measurement ranges from ±50V to ±10mV, the DI-245 provides resolution up to 1.2µV. The DI-245 supports J, K, T, B, R, S, E and N type thermocouples.

 

Additional Reading:

First Impressions of the DI-149 Data Acquisition Starter-Kit