DATAQ Instruments Application Notes and News

Sub-zero Thermocouple Measurements

Sub-zero thermocouple measurements

Figure 1 — Model DI-245 measurement ranges by thermocouple type.

Looking at the specs of a typical thermocouple data acquisition system might be a little misleading when it comes to interpreting temperature measurement capability. For example Figure 1 is a snap-shot of the thermocouple  measurement range for our model DI-245 voltage, mV, and thermocouple data acquisition system taken directly from the product’s data sheet. If you believe that measurements of sub-zero temperatures can be accomplished using almost any thermocouple type as implied by the table, you can be forgiven. One of the best kept secrets in the instrumentation world is that sub-zero thermocouple measurements require thermocouples that are specially qualified for that application.

The Sub-zero Thermocouple Measurement Problem

By “sub-zero” I mean any temperature measurement that is less 0 °C. It is generally not possible for thermocouple manufacturers to provide alloys that operate both above and below zero in the same thermocouple wire. And since the vast majority of thermocouple applications are for measurements above zero, that’s where the bulk of thermocouples are guaranteed to operate. Thermocouples for the substantially fewer sub-zero applications must be ordered specifically for that purpose. So, although instruments are designed to make the sub-zero measurements the weak link is the thermocouple itself, especially if it has not been specifically designed for such use. Unfortunately, the danger is that an unqualified thermocouple gives the appearance of working below zero but is actually generating large measurement errors. Likewise, a thermocouple that is qualified for sub-zero work may generate large errors above zero. So, if you make measurements both above and below zero, be sure to have a procedure in place that identifies one thermocouple qualification from the other.

Thermocouple Types for Sub-zero Work

Should you need to perform sub-zero work, generally certified type E and T thermocouples are used in that application. Other thermocouple types exhibit poor characteristics, like becoming brittle, succumbing to corrosion, or generating an exceedingly low EMF at cryogenic temperatures. 

Any reputable thermocouple supplier should be able to provide pricing and availability for thermocouples that are certified for sub-zero work If that’s what you need, be sure to convey so at the time of your order to ensure accurate measurements using our products or anyone else’s.

Additional Reading:

How To Power Multiple 4-20 mA Sensors

We’re often asked how to power multiple 4-20 mA sensors using a single power supply. While it is possible to do this, the usual cautions apply regarding ground loops and other subtleties. Readers who are new to measurements using sensors with 4-20 mA process current outputs should refer to our earlier article that explains basic concepts and configurations.

Multiple 4-20 mA Sensors, One Power Supply

So, you have multiple 2-wire sensors with 4-20 mA outputs and only one power supply. How can you make this work? Use this step-by-step process:

  1. Take an inventory of the minimum and maximum power supply requirements for each sensor. Choose the highest of the minimum and lowest of the maximum values of all sensors. Then pick a power supply voltage that is roughly half way between these two figures. For example, if the highest of the minimum power supply voltage for five sensors  is 10 V, and lowest of the maximum power supply voltage is 20 V, pick a power supply voltage of about 15 V. The actual value isn’t critical provided that you give yourself breathing room of a couple of volts or so from the two extremes.
  2. Multiply the number of 4-20 mA sensors to be powered by 0.02 and add 20%. This is the maximum current that the power supply is required to deliver in amperes. Again for five sensors, this value is 5 × 0.02 × 1.2 = .12 Adc, or 120 mA.
  3. Unless the instrument used to make the measurement has built-in shunts, you’ll need to add these externally. There are correct and incorrect placements depending upon the instrument, so refer to our earlier article here for complete information.
  4. Connect your sensors, power supply, and shunts (if required) as shown in Figure 1, where:
    • “E” represents the power supply
    • “R” is the shunt resistor. Replace “R” with an open circuit if the instrument has built-in shunt resistors.
    • “V” is the signal connected to the instrument.

That’s all there is to it. Using these guidelines there is no practical limit to the number of 4-20 mA sensors that can be powered by a single power supply, saving space and money.

Schematic of two or more 2-wire 4-20 mA sensors powered by a single power supply.

Figure 1 — Schematic of two or more 2-wire 4-20 mA sensors powered by a single power supply. (click to enlarge)

Active USB Extension Cables Limit Data Loss

Perhaps you have an application that requires your USB-connected data acquisition system to be positioned further from the PC than the 2 to 5 meter maximum USB cable length specification. The USB Active extension cable allows you to position your USB-connected data logger up to 15 meters (almost 50 feet) from the PC.

Active USB Extension Cable

As signals travels through a USB cable, they gradually lose strength, or attenuate. The further the signal travels, the weaker it gets. The end result is data loss. The USB Active extension cable prevents data loss by buffering data entering and exiting the cable. With data transfer rates up to 480 Mbps and no external power required the Active USB extension cable supports both high speed and low speed devices.

Active USB Extension Cable

Using a DATAQ Instruments DI-155 data acquisition starter kit, connected via a 10-meter (almost 33 feet) USB Active extension cable, we were able to record data at sample rates up to 10 kHz, gap free.

Changes to the Built-in Temperature Alert Server

There have been some changes to the server, built into the Temperature Alert TM-WIFI350 LAN-based temperature and humidity data logger. In the past, when typing the IP address of your TM-WIFI logger into a web browser, you were directed to ‘Developer Mode’. In Developer Mode you can set alarms, change connection parameters and enter email notification information. Data is stored locally in developer mode.

Temperature Alert server mode

The most recent version of the Temperature Alert server now directs you to ‘Sensor Cloud Mode’, where you’ll be forced to create a free Temperature Alert cloud account. In Sensor Cloud Mode, data is stored to the Temperature Alert Sensor cloud, where it can be accessed from any PC with an Internet connection. As with Developer Mode, Sensor Cloud Mode allows you to set alarms, view real-time data and enter a single email address where alert notifications can be sent. For a fee, you can send alerts to multiple email addresses, and receive periodic reports.

To avoid having to create an account, click the ‘Switch To Developer Mode’ link, located in the lower right-hand corner of the screen.

Temperature Alert server mode

Additional Reading:

Flood Sensor for Temperature Alert

Additional Features for the Temperature Alert LAN-based Temperature and Humidity Data Logger

 

Flood Sensor for Temperature Alert

The AC-FLDRJ is a flood sensor designed for use with the Temperature Alert TM-WIFI-350 LAN-based temperature and humidity data logger. Measuring just 2.5” x 3.25” x 1”, simply lay the sensor on a flat surface to detect the presence of conductive, non-flammable liquids. Built-in feet on the bottom of the AC-FLDRJ keep the sensor contacts just above the monitored surface to prevent false alarms. A center mounting hole allows the sensor to be bolted in place, for permanent installations.

Temperature Alert Flood Sensor

When the surface is dry, the sensor sends a ‘No Flood’ signal to your TM-WIFI-350. When a liquid is detected, a ‘Flood’ signal is sent. The TM-WIFI-350’s built in server allows you to configure the instrument so that an email alert can be sent when a ‘Flood’ signal is received.

Temperature Alert Flood Sensor

A second email can be sent when the liquid recedes (the TM-WIFI350 detects a ‘No Flood’ signal once again).

The AC-FLDRJ is available with cable lengths of 15, 30 and 50 feet, and will work with legacy products, including TM-WIFI220s sold AFTER January 20th, 2012 (with the latest firmware) and the TM-WIFI-330.

Additional Reading:

An Overview of the Temperature Alert LAN-based Temperature and Humidity Data Logger

Temperature and Humidity Data Loggers

 

Trouble Communicating With Your Ethernet Connected DI-720 or DI-730 EN-B

On This Page

Symptoms

Cause

Resolution

Verify that you’re installing the latest version of WinDaq

Verify that your Network Interface Card (NIC) has a static IP address

Disable any wireless connections

Verify Windows Firewall settings

Run the DATAQ IP Manager as an administrator

Make sure that your Ethernet cables are not more than 100 meters in length

Verify that your Ethernet cables are connected correctly

Reset your Network Interface Card (NIC)

Applies To

 

Symptoms

Upon installing WinDaq and running the DATAQ IP Manager, no instruments are found.

Your Network Interface Card is not listed in the “Select Network Adaptor” window.

An “Error binding UDP port 1234” error message

 

Cause

Could be the result of one or more of the following:

You’re running an older software installation

Your Network Interface Card (NIC) does not have a static IP address

A wireless router is attempting to assign you NIC an IP address

The IP Manager is not listed as an exception in Windows Firewall settings

You’re not running the DATAQ IP Manager as an administrator

You’re using Ethernet cables that exceed 100 meters

The instruments is not connected properly

The Network Interface Card is hung up

 

Resolution

To resolve these issues follow the steps below.

 

Verify that you’re installing the latest version of WinDaq

You can download the latest version of WinDaq for your DI-720/730-ENB at:

http://www.dataq.com/support/upgrades/record/g1lev3en.html

 

Verify that your Network Interface Card (NIC) has a static IP address

As outlined in the Installation Guide, verify that your NIC (TCP/IPv4) has a static IP address.

Ethernet Connected

 

Disable any wireless connections

Make sure that any wireless connection are disabled (not just disconnected).

To do so, open the Windows Control Panel, choose ‘Network and Internet’ and select ‘Change Adaptor Settings’.

Ethernet Connected

Right-click on the Wi-Fi connection and choose ‘Disable’

Ethernet Connected

 

 

Verify Windows Firewall settings

Make sure that the DATAQ IP Manager is allowed through the Windows firewall, for both Private and Public networks.

Ethernet Connected

To do so, open the Windows Control Panel, choose ‘System and Security’ and select ‘Allow an app through Windows Firewall’.

Select both the ‘Private’ and ‘Public’ checkboxes.

 

Run the DATAQ IP Manager as an administrator

Right-click on the ‘IP Manager’ shortcut and choose ‘Run as administrator’

Ethernet Connected

Make sure that your Ethernet cables are not more than 100 meters in length

The Ethernet cable connecting your DI-720/730 EN-B to the PC and ones between synced units cannot exceed 100 meters in length.

Ethernet Connected

Verify that your Ethernet cables are connected correctly

The “Toward PC” connection on the back of the first synced (unsynced) DI-720/730 EN-B should be connected to the Ethernet port of the PC or network. The “Toward PC” connection of the second synced unit should be connected to the “Expansion” connection of the first synced unit, the “Toward PC” connection on the third synced unit to the “Expansion” connection on the second synced unit, etc.

Ethernet Connected

Reset your Network Interface Card (NIC)

To reset your Network Interface Card, open the Windows Control Panel, choose ‘Network and Internet’ and select ‘Change Adaptor Settings’.

Ethernet Connected

Right-click on the network connection and choose ‘Disable’

Ethernet Connected

With the connection disabled, right-click again and choose ‘Enable’

Ethernet Connected

Applies to

All DI-720, DI-722 and DI-730 EN instruments, the DI-785, DI-788 and the DI-5001-E

Die Cushion Qualification

DATAQ Instruments was recently mentioned in Evaluation Engineering magazine‘s special report on data acquisition systems. The feature focused on applications in machine condition monitoring, which is an area that is very popular for users of our equipment. So, we thought we’d publish an overview of it here for our readers. The specific application was monitoring the condition of a die cushion.

What’s a Die Cushion?

As its name implies, a die cushion is a device attached to a metal press to absorb and distribute the force of the process. This activity serves to ensure a more uniform pressure over the die blank and throughout the press’s stroke. When properly configured, a die cushion enhances yield, quality, and repeatability of produced parts.

Figure 1 -- The Advanced CODAS integration utility is only of many analysis functions that may be applied to WinDaq-acquire data.

Figure 1 — The Advanced CODAS integration utility is only one of many analysis functions that may be applied to WinDaq-acquired data. Each is an easy-to-use, non-programming point-and-click utility.

Die Cushion Measurements

Our customer is a press manufacturer, and wanted to qualify the function of a die cushion in a particular application. The die cushion was a hydraulic device, so a pressure sensor with a 4-20 mA output was fitted to it and connected to a DI-718B-U data acquisition system running WinDaq data acquisition software. Conditioning and excitation for the sensor was provided by a DI-8B42-01 amplifier, that was installed inside the DI-718b instrument, resulting in a compact and powerful data acquisition solution.

Figure 2 -- Screen shot of acquired pressure waveform (top), and other two analysis waveforms generated by Advanced CODAS analysis software.

Figure 2 — Screen shot of acquired pressure waveform (top), and other two calculated waveforms generated by Advanced CODAS analysis software: Integrated and differentiated pressure (middle and bottom respectively.) Diamonds show the peak values of each, which are used to characterize die cushion performance.

Only one measurement was acquired by the instrument, but a pressure curve by itself was not enough to qualify die cushion condition. To gain the necessary insights, post processing was required and supplied by DATAQ Instruments’ Advanced CODAS waveform analysis software. That package allowed meaningful post-acquisition analysis by generating two calculated channels derived from the original pressure waveform: its integral and derivative.

Integrated Die Cushion Pressure

The original die cushion pressure waveform was passed through Advanced CODAS’s integration utility to produce an output that was aligned in time with the pressure signal, but could be interpreted as the amount of work done by the die cushion. It is extremely difficult to glean die cushion work from the pressure waveform alone. Variations in the pressure waveform from press cycle to press cycle, and from part to part can be extreme. However, integrating the pressure waveform accounts for all of these variations by producing a result equal to the area bounded by the curve of the pressure signal with associated engineering units of psi-seconds. This terminal value of the integral before reset can be viewed as the total amount of work done by the die cushion for the press cycle. It follows that a die cushion that has failed in some manner that affects the pressure signal will also affect the total work done by the die cushion over the press cycle. If the die cushion develops a leak, overall pressure will decrease, which will immediately impact total work done by the cushion resulting in a lower terminal value.

compressed die cushion

Figure 3 — A compressed view of acquired and calculated data showing multiple press cycles, and demonstrating the running calculation capability of Advanced CODAS analysis software.

The utility of the integrator facility provided by Advanced CODAS is enhanced by the multiple reset methods that can be configured. In this situation, pressure always returned to zero after a press cycle, so the integrator was configured to reset upon zero crossing of the pressure waveform, which ensured automatic and meaningful measurements per press cycle.

Differentiated Die Cushion Pressure

The total amount of work done by the die cushion is only half of the story. Also of great interest is the stress applied to the device during press cycles. This quantity is revealed by another Advanced CODAS utility that differentiates the pressure waveform with respect to time. Scaled in units of psi/second, this result quantifies the abuse absorbed by the die cushion, caused mostly by large, initially applied pressures. Since derivatives tend to produce noisy results, Advanced CODAS allows derivatives to be calculated over adjustable window sizes. The derivative of the pressure waveform discussed here responded well to a window size of 7.

Putting It All Together

Figure 1 shows the Advanced CODAS configuration application where various calculation functions and options are selected and applied to acquired data. It features a point-and-click, non-programming user interface for ease of use. Shown is the Integration screen with all of its reset methods.

Figure 2 is a screen capture of only one cycle of the analysis result. The top-most waveform is acquired die cushion pressure in units of psi. The middle waveform is the integral of pressure, reset upon zero-crossing of the pressure waveform. Its units are psi-seconds, and the total amount of work performed for this single press cycle is the peak value shown in the diamond, about 620 psi-sec. The bottom waveform of Figure 2 is the derivative of pressure. In units of psi/second, the peak value of approximately 104,000 psi/sec is shown in the diamond and represents the most extreme stress experienced by the die cushion in that particular cycle.

It is important to note that Advanced CODAS is a waveform analysis package that produces a running calculation. Figure 3 is a more compressed view of the analysis showing that calculations are applied automatically across multiple press cycles.

Additional Reading:

Advanced CODAS Analysis Software

DI-718B Data Acquisition Systems

DI-8B42-01 4-20 mA Transmitter Amplifier

All DI-8B amplifiers

 

Same Great Content with a New Look

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

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

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