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Collecting Parachute Test Drop Data

Collecting Riser Force Data

Due to the wide variety of riser and load link configurations that are possible, Industrologic, Inc. does not offer parachute riser and load link products. We do, however, offer PDAS-3 data loggers designed specifically for parachute test drop work, and SGAMP-2 signal conditioning amplifiers designed specifically for strain gauges installed on your load links.

We can also provide Custom Wiring and Enclosures for amplifiers and load links for your data acquisition system. If you have any questions related to how to go about developing your own riser force data collection system, please contact us.

Collecting Parachute Riser Force Data With Load Links describes the process of using a load link of your own contruction (or a commercially available load cell), an Industrologic SGAMP-2 strain gauge amplifier to convert the signal to a voltage, and an Industrologic PDAS-3 data logger to collect the raw voltage data from a riser mounted link or cell. It also describes the process of converting the raw voltage data to force data using techniques unique to parachute riser force measurement.

Constructing Your Own Load Links

Constructing your own load links shows some examples of some typical load links used by our customers and colleagues, including details of load link construction and wiring.

If you would like to know more about strain gauge measurement, Vishay Precision Group Micro-Measurements Division has a great deal of technical information about strain gauges in their Knowledge Base.

Commercially Available Load Cells and Load Links

A number of companies provide load cells/load links in a variety of force ranges. These devices are provided with specifications that indicate the force range in which the device should be operated, and calibration data for the output of the device based on the force applied and the voltage used to provide excitation voltage to the device.

Load cells/load links contain strain gauge bridges which require signal conditioning with devices like our SGAMP-2 strain gauge amplifier in order to provide a voltage output that allows them to be connected directly to voltage input data acquisition devices like our PDAS-3 data logger. (Some data acquisition devices, however, have inputs designed specifically for strain gauge bridges.)

When load cells/load links are used with signal conditioning circuits, you must determine what the voltage output of the signal conditioning circuit will be based on the circuit gain and the calibration data from the load cell/load link, (or a calibration can be done with actual force applied to the load cell/load link under a variety of conditions.)

Some load cells/load link products have options that include internal signal conditioning with voltage outputs. Internal signal conditioning has the advantage of your being provided calibration data for the voltage output of the device by the manufacturer.

The following is a partial list of companies that offer load links and load cells. If you decide to use commercially available load cells/load links, Industrologic can provide custom wiring and cabling of your load cells/load links and amplifiers to your data acquisition system.

(Searching the web with the search phrase "link load cell" will provide many more sources.)

Collecting Accelerometer Data

We suggest that you read a short article from the Parks College Parachute Research Group titled The Collection and Interpretation of Accelerometer Data in Parachute Systems.

There are a wide variety of accelerometers available based on several technologies. We have experienced a great deal of success and ease of interfacing to our data acquisition systems with the following units.

They are both based on capacitive micromachined accelerometer chips, are +5 volt powered, have a +0.5 to +4.5 volt output, and respond to accelerations down to zero HZ. They are available in several full scale acceleration ranges.

Sample PDAS-3 data files using accelerometers, and the PDAS-3 download/graphing program can be downloaded on the PDAS-3 software page.

Collecting Rate of Descent Data

Industrologic, Inc. offers a vertical speed indicator/voltage output altimeter designed specifically for parachute test drop work, and that easily interfaces to our data logger. This product offers the ease of recording the altitude/vertical speed at the same time you are collecting other data and having it available in the same data file.

A sample PDAS-3 data file using the VSI-1000, and the PDAS-3 download/graphing program can be downloaded on the PDAS-3 software page.

There are, however, other ways to determine the descent rate of a parachute, and some entirely mechanical methods work quite well.

  • If you have the ability to attach to the load a long line of a known length and with a weight on the end, you can use a stopwatch to determine the time between when the weight reaches the ground and when the load reaches the ground, and calculate the rate of descent from that. (Note that the weight on the end of the line must be small compared to the weight of the load, or else the load will descend slower after the weight lands.)

  • The above method can be used in conjunction with a data logger, that is, switches (such as mercury switches) can be installed in the suspended weight and in the load. When these switches are activated by their respective landings, the time between their signals can be determined by the data logger sample rate to calculate the rate of descent.

  • An easy to read and clearly marked altimeter can be placed on a platform with a video camera facing it and recording the altimeter movement during descent. Timing and distance calculations can be easily done later while viewing the video.

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