How to connect accelerometer to USB-9233?

[golubovski]

Colleagues,

 I need to connect an accelerometer from Analog Devices (ADXL78) to an USB-9233. The problem is, the ADXL78 has 2 Vdd inputs and an output (acc reading) and USB-9233 is the conditioner that reads and supplies current via the same BNC connector. I am not familiar with this field of electronics and confused how to combine both power supply for the sensor and reading its output via the same connector. I guess I'll have to build a circuitry to accomodate both functions and need assistance on this.

Also, sensitivity is about 40mV per G which makes about 2V and USB-9233 inputs ±5V. How to amplify the ±2V output of the sensor to the desired range of ±5V, provided the above priority problem is solved.

Thanks in advance,

[golubovski]

Sorry, I forgot to upload the PDF, here it is!

[Henrik_Volkers]

First problem: the 9233 is build for IEPE (ICP) Sensors and the ADXL78 isn't 

According to page 11 in  9233 User manual + spec the current source and AC Filter are always enabled.

Since your Sensors output is 400µA you would need an OPamp as Voltage follower (and external powersupply or spend another input as a powersupply) to 'simulate' an  IEPE

Message Edited by Henrik Volkers on 10-27-2008 11:00 AM

[Seth_B.]

Golubovski,

Unfortunately, the NI 9233 module is not compatible with this sensor.   This is because, as Henrik said, the 9233 is designed for use with IEPE accelerometers.  This is noted in the 9233 documentation.  The 9233 & 9234 provide both the signal conditioning and current excitation to the sensor.  This allows us to use AC coupling to eliminate any power line noise, insuring more accurate measurements.  Otherwise, your accelerometer output signal will vary with any power supply noise provided with 

However, the Analog Devices (ADXL78) sensor performs signal conditioning within the sensor.  Also, the ADXL78 sensors require a voltage excitation, instead of a current excitation.

In order to use the USB 9233 for accelerometer measurements, you should use IEPE compatible accelerometer.  Otherwise, you will need to provide your own external voltage excitation and use a different module (one capable of strict AI Voltage measurements such as the NI 9239) to read the acceleration.  Please note that you will need to take any noise due to your external excitation into account.  Handling that noise would definitely be an issue to bring up with Analog Devices.