Reading -2 to -18 volts Analog Input

[ssingh1]

Dear Friends,

We are using PCI-6221 for data acquisition which is having voltage input range of +-10 Volts.

Recently we had a requirement of connecting new type of sensors with output voltage range of -2 to -18 volts.

Is there a way to connect this input the 6221 card?

Also, Is there any other DAQ Card available for this type of input range?

Thanks

Shourya

[AdnanZ]

In order to bring the voltage level into the range that the board can measure, you must use an attenuator. A voltage divider will suffice as a simple attenuator, however an op-amp with fractional gains may provide better impedance characteristics.

You could visit the following link to find a board that fits your range:

http://sine.ni.com/nifn/cds/view/main/p/sn/n11:7601,n36:19/lang/en/nid/1036/ap/daq

[ssingh1]

Dear Adnan Z,

Thanks for your email.

We will be considering the use of op-amp as suggested by you to reduce the voltage input range. However no board for this input range seems to be available with NI.

Shourya

[ChrisR.]

If the transducer is not already referenced to ground (i.e., it is floating), then you could refer it to one of the board's analog outputs, which you could set to +10V.  Then the output of the transducer would be -2 to -18 volts with respect to +10V, or ±8V with respect to ground, and you could measure it directly with the board.

Can you share more about the transducer?  Do you have a manufacturer name and model number?

Chris 

[ssingh1]

Dear Chris,

Thanks for your idea. Yes it seems to be a good Idea to connect +10 Volt output to referance for reducing the effective gain.

The sensors are Eddy Current Proximity probes which are indeed floating. Please see the attached Manual.

Shourya