Data Logger Components

This picture shows the dual axis accelerometer board that I designed. This accelerometer is based on a thermal mems accelerometer technology from Memsic Corporation. (www.memsic.com) and two of these boards mounted in a chassis form the basic triaxial accelerometer used for this data logging system.  As can be seen in the picture the accelerometer board is about 1.5 inches square, about as small as I could make it.

The reference design from Memsic was modified to extend the sensors normal linear range from 30Hz to 200 Hz at the 3db down. Due to the requirement for an additional external filter I decided to hand wire the boards. The leads prior to assembly in the triax chassis are shown.

This shows the triax assembly prior to closing up the potting and closing up the sensor housing. The basic triax accelerometer has one dual axis board mounted on the bottom the housing and one on the side. The orientations of the accelerometers are such that there is one channel each for fore and aft axis (x), one for the vertical axis (z) and two channels for lateral axis(y). (I had to pick one for duplication so that was my choice (lol)).  The rough edge board mounted on the side with the ZY axis board is a final stage output filter that I made to move the 3 db point to 180 Hz.

I am providing two accelerometers for this set of tests. One to be mounted on the engine and the other on the airframe. Using this technique, I should be able to develop a transfer function that will provide additional information about the mount characteristics and how much vibration energy is being transferred to the airframe. The accelerometer on the engine is a +/- 2g triax accelerometer and the airframe accelerometer is a +/- 1g accelerometer. The mounting plates on the accelerometers are ¼” aluminum with a 5/8” (I think) mounting hole. The engine accelerometer is designed to mount on one of the top engine cover studs and you may use a thin paper gasket under the mounting plate to keep from marking your top cover. DO NOT use a rubber or other soft gasket material as it will absorb the vibrations we are trying to measure.

After much searching and trying to keep the test process as simple as possible, this is the hookup that I developed for the RPM sensor.  The inductive pickup is from an inductive timing light that I had in the garage. I developed a Frequency to Voltage circuit that will take the impulses from the high tension lead (big wire… not points) and provides a linear analog voltage from 0.2 volts at 600 RPM to 4 volts at 3600 RPM based on a six cylinder engine.

Here we see everything that needs to be mounted on the engine and airframe… Just three devices> I made it as easy as I could for the builders as the goal is to collect data…. Not learn instrumentation processes and techniques.  I still welcome any additional ideas for mounting as long as the mount technique is mechanically solid.

The data logger is a high speed data logger from IOTech (www.iotech.com). This is one of their older units but it still works great and I could afford it….(g) The little bread board in the upper right corner is the power supplies for the Accelerometers and for the Frequency to Voltage (F to V) converter. The F to V is also mounted on that board and consists of the two little chips and the associated capacitors and resistors.

I think that I said once in an email that I was not much of a fabricatior and these photo’s prove it. However it is functional. The accelerometers are clearly marked as their respective connections. The computer cable is connected to the printer port on the laptop and once all of the connections are made you just have to run the software (more on the software later)

There we have it. The entire logger system consists of five pieces, a laptop, the logger and three sensors.  I will be providing more on the operation of the software and a couple of photos of the sensors mounted on a Corvair engine shortly.

  The Mad Scientist's Workshop