DC LVDT Measurment with CompactDAQ

[ghattas.ak]

Hello,

I am currently working on getting reading from an LVDT for a project the present model is the DC LVDT model Omega LD620-25

As per it's datasheet the model requires an excitation voltage of 10-30V and a maximum current of 25ma

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

as for the data aquisition modules available: the NI 9237 and the NI 9220 using a compactDAQ module

as the NI9237 has an internal power of 150mW the maximum current obtained is 15ma, will it be enough to use?

the NI 9220 will be used for data aquisition but does not provide any excitation ports!

as for the another solution I was thinking of using a normal 12Vdc 100ma AC-DC adapter with a variable pot or a voltage divider circuit to provide the needed voltage

but I have several concerns regarding grounding the circuit. in such scheme I will have two independent grounds!

What will be the best solution to connecting the LVDT module to the NI 9220 and providing an external excitation source?

Thank you

[Izzzzz · Accepted solution]

Hello ghattas.ak

Consider the NI 9218. It can provide exictation of 12V at ~50mA per channel and read the 5 or 10V output from the DC LVDT. To use this 12V excitation a 9-30V power supply must be connected to the Vsup pins. As you mentioned, you can also use the NI 9220 with external excitation. The NI 9237 measurment range of +/-25 mV/V does not cover the 5 or 10V output from you sensor. 

Cheers,

Izzy O. 

Staff Product Support Engineer

National Instruments 

ni.com/support

[ghattas.ak]

Hello,

Thank you for the answer, I will get a regulated AC/DC adapter of 12v and 500ma to externally power the DC LVDT there will be seperated grounds but as per the datasheet the input and output are internally isolated therefore that shouldn't cause any problems as for the data aquisition part I will be using my NI 9220 module

Thank you

[ghattas.ak]

Hello Again,

I have connected the LVDT to the 9220 Acquisition module with external excitation of 11.5 volts ( measured) the external adapter is connected to a Voltage regulator that output the 11.5V excitation

The connected signla sig+/- are connected to the 9220 differential input on channel 0

The circuit ground is the regulators ground

I cannot get a voltage variation from the LVDT the output is around 10.2 volts and stays that way even if a displacement occured

The following screenshots shows two cases:

1) the circuit ground is connected to the com port of the 9220 and the regulators

2)the circuit ground is connected to the regulators ground and only a0+/- are used on 9220

the screenshot shows LVDT wires