Somehow we tend to enjoy new things on a fixed place first, and then we want to take them with us at any time. Just think of the fact that twenty years ago everyone had a landline phone at home, and today even our grandparents own a smartphone. Or about traditional Viennese coffee house culture that was supplanted by a takeaway-coffee culture. It’s kind of obvious that around 15 years after the presentation of the first digital density meter for the lab, a portable version was launched. Learn more about the story of field measurements, their pros and cons, and special instrument features in this post.
The benefits of portable digital density measurement were obvious from the start: there is no need to transport the sample to the lab, and you can instead do an immediate quick measurement directly on-site at the sampling location, no matter where you are and where the sample is. As it always is with innovations, in the first years persuasion was necessary and the product had to prove its worth. And it did.
Special instruments for special requirements: Explosion-proof instruments
Only two years after the first portable density meter was launched, the first explosion-proof version was announced and ready for sales. Intrinsically safe portable density meters went through a special certification procedure, ensuring that they cannot cause any fire or explosion, not even in the case of an instrument error. Such special instrument versions are a must-have for companies measuring flammable or explosive samples and/or in explosive atmospheres (EX zones) to protect employees involved in the measurement tasks as well as the company’s property.
Contemporary witnesses of portable density meter history
The first portable density meter – honored with the Austrian Innovation Award – was ready for only one type of field application: density, relative density, or concentration measurement. The instrument sucked the sample into the cell via a vacuum caused by pressing the bellows and showed the digits the way we are used to from a calculator. I personally call it ‘the phone’ because it looks like one of the first huge cell phones. In old marketing material I found a nice statement: “The device has been constructed for left-hand filling and measuring, thus leaving the right hand free for writing”, as there was no storage function available yet. An Ex-proof version was announced two years later.
DMA 35 Dip-in
In 1983 the idea of a dip-in density meter was born. The density sensor was decoupled from the display unit, allowing the operator to put the sensor into a tank to measure at any position of the tank. Via density measurement at different heights, users could identify any stratification of sample within the tank that could appear during storage of samples or they could check during the blending of substances whether these were already properly mixed. The challenges: cleaning the sensor and connection cable after the measurement and the fact that users tended to handle the cable and sensor like a cowboy would handle their lasso. Run for cover!
DMA 3000 & DMA 3000 Dip-in
I’m blue Da ba dee da ba di! But actually the DMA 3000 (Dip-in) was there six years before the song you now have in mind. It already allowed for switching between several concentration units and storage of 200 data points. Printouts and exports of data to a PC via RS232 interface were also enabled. The handle contributed to more convenient carryin and operation.
Yellow and Red are not only starring in an M&Ms advertisement but are also the colors of the following instrument generation. DMA 35N allowed for storage of 1024 results, installation of custom concentration units, and had a completely new pump design. “It’s small, so it easily fits into hard-to-reach places without bending or stretching, and the new pump is a dream … no bellows that split open, no squeeze bulbs to tear.” says the brochure from 1997. The instruments were improved from generation to generation, based on customer feedback and long-term experience.
DMA 35 (again!)
The design, called ‘dog leash’ internally at Anton Paar, stayed with the latest version of DMA 35, impressing users with a clearly structured and intuitive user interface, wireless data transfer via IrDA, automatic sample identification via RFID tags stuck to sampling locations and, of course –the Ex-certified versions for use in explosive atmospheres and for measuring hazardous samples. Find more information on the instrument here.
In 2014, two colleagues of DMA 35 were launched: portable density meters with a clear focus on measuring distilled products without added sugar. Snap 40 is designed for home distillers. Whereas home distilling (or producing moonshine) is illegal in some countries, for example in the USA, it is very common in many other parts of the world to process private fruit harvests into juices and spirits. Whereas Snap 40 provides results with an accuracy of 0.2 %v/v, Snap 50 measures alcohol accurately to 0.1 %v/v and is designed for microdistilleries. Several pharmaceutical companies also love the highly accurate alcohol meters for checking the pure ethanol in intake control.
Pros and cons of on-site measurement with a digital portable density meter
- The sample can be taken directly from the sampling container using a built-in pump and is measured directly there. You do not waste time by transporting the sample to a lab.
- The instruments require a very low sample volume (usually around 2 mL) for the measurement.
- The measurement is incredibly quick: the instrument shows the result in a few seconds. Many users dealing with a large number of samples per day report a reduction from eight hours measuring time with a hydrometer to only one hour with a portable device.
- Automatic temperature compensation: measurements are done at the given temperature and results are automatically compensated for the temperature influence. It is not necessary to correct the temperature influence manually using a table.
- Some portable density meters even provide some sample identification: results from samples taken in the field can be uniquely allocated to the respective sample or sampling location.
- If an RFID interface is provided by the instrument, switching between different sample IDs is done in a second. The sample information as well as the measuring method to be used for the measurement is stored on an RFID tag mounted on the sampling location. Before the measurement, the information is read from the tag using the portable density meter and the measurement is performed according to the information coming from the tag. Not bad, right?
- Most instruments can internally store a list of results, which you can print or export to a PC later on.
- One digital instrument replaces a whole set of glass hydrometers, as there are many concentration units preinstalled and for all of them the full relevant measuring range is covered by one and the same instrument.
- Easy handling: you do not need expert staff to handle the instrument.
- Robustness: the instruments are prepared for field environments (look for the protection class! It will tell you whether the instrument is leak-tight. IP 54, IPx4 are good choices). Protective measures like rubber housings, wrist-/or carrying straps, suitcases, etc. are also available.
- Be careful about the temperature influence! Portable digital density meters do not have any temperature control, so the measurements are performed at the given temperature. However, the instruments provide an automatic temperature correction, meaning that the measurement is, for example, performed at 24.7 °C but the instrument already corrects the value for the temperature influence and shows the corrected result for the reference temperature of 20 °C.
- Due to the lack of temperature control, portable density meters are usually not as accurate as benchtop lab instruments. One additional digit in accuracy might save you thousands of Euros when it comes to measurements relevant for customs and taxes, process and raw material optimization, or filling volume control. Make sure to use a sophisticated lab instrument in addition to the portable instrument for such critical measuring tasks.
- Although they are prepared for harsh environments (leak-tight sealing for many models, protective measures, etc.), digital portable density meters are still sensitive measuring devices. If the instrument containing a glass measuring cell is dropped, the measuring cell may break. Always make sure to use a wrist band or carrying strap as well as a rubber housing to protect the instrument in the best possible way.
When talking to users of a portable density meter, I often get very surprised reactions after telling them about the wide range of applications these instruments are used for. It is somehow natural that we only have our type of business in mind, but it gave me the idea to quickly show some different applications of the instruments. You may also be surprised.
Five typical applications for portable density meters
No matter whether we are thinking of a soft drink bottling plant or a chemical manufacturer: a portable density meter helps to check whether delivered goods are of the correct quality and type, helps to do quick blending checks, and will speed up measurements on intermediate products during production.
Are you already measuring on-site?
Why did you decide to do so and what was the benefit most relevant for your daily work?
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