I'm pretty new to ODS & Modal, but I now have the proper tools (ME'Scope & Zonic 618) to collect and analyze ODS & Modal data.

I'm interested in what kind of transducers you are using in the field?

For my first modal job, I used a Dytran 3143D1 tri-axial accelerometer, mounted on a custom (internally made) aluminum block (1" cube). The mount is drilled & tapped to accept the accelerometer and three magnets. One problem I noticed was that the accelerometer uses a small 4-pin cable, that doesn't have any strain relief. I'm worried about the durability of this setup.

What kind of tips can you offer?

Steve

Interesting combination, Steve. That will do the trick. I use a CSI model 906 magnet (cube) with three targets mounted (1 screwed and 2 glued). I use a standard top exit accelerometer. I also use a spot facer to drill and tap a mounting location for the other stationary accelerometer. It's frustrating to tug on the cable and dislodge it. I use a 15 foot cable on the stationary accelerometer and a 4 foot cable on the roving one. This works for 90% of the machines I do. If the machine is larger, I use a longer cable on the roving accelerometer.
For modal jobs, I use the same stationary setup and try to rove the hammer.

This message has been edited. Last edited by: Jon McFadden,

Here is a picture of my transducer setup, similar to Jon's but different due to the magnets and tri-axial accelerometer.

Hi Steve,
I'm curious why you used a 6-32 screw instead of the standard 1/4-28 accelerometer (like the Dytran model 3063B)?

Jon - The 6-32 is the standard screw for the 3143D1. You can't see it, but the mounting hole through the accelerometer has a counterbore. A 1/4-28 screw won't fit.

The cube is drilled/tapped on 3 sides for the 6-32. On the opposite 3 faces, it is drilled/tapped for 1/4-28.

I choose aluminum to keep the weight down because I use the same cube to functionally test the tri-axial accelerometers on a shaker prior to installation (permanently mounted).

Steve

Hi Steve,
Let me re-phrase my question. Why did you use the Dytran 3143D1 instead of the Dytran 3063B? The only difference I can see is the size screws they use.

We have the 3143D1 permanently installed on a number of motors. The selection of that transducer was before my time here. At this time, we are just trying to stay consistent. It's much easier to get an accelerometer from our stock than trying to get a purchase requisition fulfilled.

The 3063B is a bigger (twice the size) of the 3143D1.

Steve

I assume that adding a triaxial base with 3-magnets to a triazial accelerometer is an attempt to keep the accelerometer orientation consistent with the structure's coordinates for any/all measurement points. While I assume that this configuration can or has worked for some situations, I do not like it for the following reasons:

1) May be too heavy for some structures
2) May affect frequency response for tests at higher frequencies
3) It may not accomodate mounting on all measurement surfaces (suppose surface was above the accelerometer?)

If a magnet mount was desireable (instead of adhesive or wax), then I use a single magnet directly attached to the accelerometer. I then change the measurment point definition, as needed, for the +/- X-Y-Z orientation directions for each of the three data channels.

I am not knocking the 3-magent base as a bad idea, but it's just not good for me.

Walt

Hi Walt,
I normally use a single accelerometer, but there are times when you can't get a reading without adding another surface. I use my "cube" on long rails where I am taking an axial reading and there isn't a surface to collect the data from.
Before I modified the "cube", I would omit the data in that axis.