How to Connect MEMS Triaxial Accelerometer, Endevco 7284A?
I am trying to wire up my Endevco 7284A triaxial accelerometer to DSUB9 connectors. All three axes appear to share excitation. I intend to wire the first channel/connector as differential voltage input with 5V excitation. The second and third channels/connectors I will wire as differential voltage input with no excitation. I have a non-isolated Sirius HD-STGS board as well as an isolated Sirius XHS board with UNI inputs.
For any of the channels, do I need to make the GND connection to pin 4 represented by the dashed line? Would i connect IN- or IN+ to Gnd, possibly with resistors? The manual has this comment "Use only when sensor Output (+) and Output (-) are referenced to Gnd. Gnd must be connected." Do I need to bond the GND pins for all three channels together? Should i bond all 3 excitation- channels together? Are there any differences if i am using an isolated vs non-isolated board? Are excitation- and GND internally tied together (what about isolated vs non-isolated boards)?
I intend to connect the shield of the cable to the metal housing of the DSUB9 shell. The body of the accelerometer is not connected to the shield of the cable. The accelerometer itself is mounted to a large metal frame. The metal frame is not earth grounded. Should I connect the metal frame to the earth connection on the back of the Dewesoft board? I almost always power my Dewesoft boards using a large battery bank/power inverter, but the battery bank itself is not earth grounded. I guess in theory, the entire system is "floating".
Diagram for channel 1.
Diagram for channels 2 and 3.
Sensor Diagram.
Dear Mitch,
thanks for contacting us. For both of you types of amplifiers this sensor should be connected as on the wiring shown on the figure below:
In software Channel 1 should be set to Bridge to provide the sensor with excitation and channels 2 & 3 will be set to single-ended voltage measurements.
Channel 2 and 3 setup should be set to single ended, not differential.
Regarding whether to connect the DAQ's earth terminal to the ungrounded metal frame, it heavily depends on the frame's environment. Because you are powering the system with a battery, your setup is floating and inherently well-protected against ground loops. However, if that metal frame is near other electrical devices or machinery, tying your DAQ to it might actually inject unwanted noise into your system.
To be absolutely sure, I recommend a quick test:
- Start with the frame completely disconnected.
- Monitor your signal using the FFT analyzer in Dewesoft.
- Temporarily connect the DAQ earth terminal to the metal frame and watch the FFT.
- Proceed with whichever configuration yields the lowest noise floor.
Please let me know if you have any other questions!
To expand on the non-isolated and isolated difference. The non-isolated has common ground across all amplifiers and isolated has each grounded separately.
After some internal talk we figured you can also change the 2. and 3. channel to differential. In this case any of these will do.