# DC-LVDT Output noise filtering

I am working with the DC-LVDT Omega 620-25

http://www.omega.com/pptst/LD620.html

I am using the NI 9220 module on a compact DAQ for data acquisition. the module supports differential inputs and single ended mode.

I am experience some trouble obtaining 3 digits of accuracy from the converted signal, the excitation voltage is 12.75 Volts (external adapter) and the reading is -5.9

Furthermore the second case was by using a single ended connection (as per the modules datasheet) single ended is achieved by connecting the signal - of the LVDT module to the COM input, I also placed a 100nF capacitor for noise filtering, I was able to get 2 digits of accuracy 1.12x.

Input is read with a continuous acquisition mode of 100 samples/second with a 500Hz frequency and a voltage range of -10 and 10 as device parameter options ( only differential mode is selectable)

In addition and since the LVDT is linear I should directly convert the voltage reading to distance but the output voltage is of different range the datasheet states that for an lvdt of -d/2 and d/2 it should outputs a -5 and 5 V readings.

I double checked on the sensitivity formula mv/V/mm Output Ripple: 0.02% FSO LD620-25 ±25 (±1.0)inch and with a range of -6 -> 6 the full LVDT range is (12V) therefore is its of 0.0024 mv/V * 12.75(excitation) = 0.0306mm

Example used: http://tinyurl.com/hrcshow

but i didn't use that as for calibration I am considering the initial read voltage to be the 0 reference and then subtracting it from each reading!

1) What is the difference between using a single- ended and differential modes for a DC output? and how can I achieve better accuracy

2)where do I use the calculated sensitivity and did I get the calculation correctly?

3)how can I eliminate additional noise (AC noise) that is affecting my measurement and what should I take into consideration for designing a filter and choosing it's type

when disconnecting the LVDT excitation voltage the modules outputs uV values that varies. considering the copper wire acts a receiver and generating additional noise I place the 100nF capacitor between the signal + and signal - terminals.

In addition, I am going to design a circuit to level shift the output voltage from -6 6 to 0 - 12 and make it a single ended output and connecting it to an arduino or a PIC (is it a good idea)?

Thank you in advance! I appreciate the help