Data Acquisition in challenging conditions: reliable testing for rugged applications

Ultra-rugged test and measurement equipment is required when testing in really challenging conditions – such as exceptional humidity, abnormal temperatures and extreme vibration – to provide precise measurement results.  Guaranteeing this high level of performance demands that data acquisition equipment is thoroughly tested before being used in the field. Using the new rugged QuantumX modules as an example, we would like to describe the respective test procedures in more detail. 

Take the term ultra-rugged. What is it about the new rugged QuantumX module that ensures operational durability and data acquisition reliability in tests taking place in all weathers and over rough terrain?

At first glance the simple provision of a sealed metal enclosure and robust connectors might seem sufficient to make DAQ equipment suitable for all environments. However, one of the first challenges is to closely examine the target applications and specific environmental conditions as these can influence the overall design of a DAQ unit. Suitable ultra-rugged target applications would include construction and mining, agriculture or marine uses whether mobile or stationary or even used in lab testing. 

Working closely with users, HBM collected typical load profiles and classified these to develop a range of filters to optimize data quality. Load profiles are a mix of amplitudes and frequencies gathered over time and they vary in combination and influence on the DAQ.

Ensuring reliability

HBM also undertook focused environmental testing by simulating physically demanding situations to ensure the reliability of its data acquisition modules for applications in harsh environments.

Developing standardized tests is a major aspect of this work since standardized tests give invaluable feedback in developing a module’s ability to provide reproducible results. Does the module for example remain fully operational when the package is cracked or a wire is broken?

Many of these reliability tests are performed in HBM’s own accredited environmental test laboratory. This is equipped with a climate chamber, electro-mechanical shock and vibration system, water basins and EMI testing facilities: specialist external test facilities were also used to provide additional performance checks.

Testing the influence of temperature and humidity

Picture: test of dew point crossing

One important design specification was the need for an extended ambient temperature range of -35 to 80 °C (-30 to 175°F) for the new rugged QuantumX modules.

Testing that the modules could function properly at these extreme temperatures was undertaken with climate chambers that examined the influence of rapidly cycling temperature changes and humidity on the units. These tests ensured continued functionality in these environmental conditions whether in transit, being stored or while in operation.  

Thermal shock tests were performed to determine the unit’s ability to withstand sudden changes in temperature. These are the most severe of all the temperature related tests as they involve rapidly changing the rate of temperature change. The modules are designed for an operational rate change of 30°C per minute. The tests are particularly critical since modules may be used in vehicle winter tests where they can be completely frozen with all power off and subsequently warmed up once the power has been resupplied.

HBM’s engineers simulate real-life conditions by exposing the module to -40 °C for three hours and then to 85°C within a short period. The temperature remains at this level for a further three hours before being restored to ambient room temperature so that the dew point is passed, ensuring any water condenses to check the effect on the module. The test is repeated a minimum of ten times.

Testing shaking and shocking

The shaking or shocking of a component or assembly is achieved through vibration testing. This is required to see how the modules will stand up when being used in field tests over very rough terrain. Damage is most likely to occur when the device vibrates at its natural or resonant frequency.

Picture: vibration testing

To ensure maximum service life, the module is mounted in a shaker or vibration system and then subjected to a vibration profile with 5 g amplitude for 35 minutes between 55 and 2000 Hz on all three directional axes. Any resonant frequencies discovered are re-tested for a further five minutes with constant amplitude of 0.06 inches. The lower frequencies of 10 to 55 Hz are swept in one minute with total tests lasting two hours in every direction. 

Picture: vibration testing – swept sine shaking

Similarly 35 g shocking amplitude was specified for the unit. For this test the module was mounted in a vibration system and shocked at 35 g amplitude for 6 ms in all three directional axes. 

Picture: shock testing

Finally the unit was subjected to a drop test from one meter and checked it functioned correctly following impact.

Testing for water, dust and dirt ingress

HBM conducts the tests in two parts. For both IP65 and IP67 the module is placed in a hermetically sealed dust chamber where a pump circulates extremely fine talcum powder. A vacuum pump is used to ensure that the module itself is below ambient atmospheric pressure. These tests were successful since there was no dust infiltration into the unit. 

For the second part of the IP65 test, the module was tested with water projected from a high-pressure nozzle for some hours while to attain IP67 the module was submerged at a depth of one meter for 24 hours. In both tests no water ingress was discovered.  

Picture: IP testing - dust chamber test

Picture: IP testing - water projected from a high pressure nozzle

Testing electro-magnetic interference and immunity

Apart from the possible influence of a ship’s radar, target applications for HBM’s latest robust modules do not demand specific EMI requirements. Nevertheless, HBM has tested electro-magnetic inference according to EN61326 and the units have been awarded a CE-mark to indicate compliance with the EMI and Low Voltage Directives.

Additional environmental criteria

Although HBM has rigorously tested its robust QuantumX modules to meet very stringent requirements there are additional criteria that were not considered essential for the design or testing of these modules.

These include:

  • Low pressure (altitude) – while the modules are fitted with a special membrane this has not been tested in low pressure or vacuum.
  • chemical, fluids susceptibility, salt
  • direct sun
  • magnetic effects
  • explosion and flammability

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Rugged measurement technology from HBM

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