voltage isolation in NI9206 channels

[Biosolutions]

Hello All,

We are having an issue, not sure what can be done.  We have the following hardware that was just purchased.

1. NI cDAQ-9188XT CompactDAQ Chassis (8-Slot Industrial Ethernet)

2. -±80 mV Thermocouple Input, 14 S/s, 4 Ch Module

3.  NI 9206 ±200 mV to ±10 V, Analog Input, 250 kS/s, 32 Ch Module

4.  NI PS-15 Power Supply, 24 VDC, 5 A, 100-120/200-240 VAC Input

The intent is that we need to measure a series string of 12 battery voltages which are each 4.2V  (50V max).   However, this this 12 cells is just really the minimum, with the possiblity of doing upto maybe 150V max rather than 50V

The thought was that the channels are differential and we could use this system to do differntial measurements across each 4.2V cell as the individual cell voltage is all we are intersted in.   However, we are now confused as someone has pointed out that the datasheet says there is no channel to channel isolation, the 600V isolation is only across the 'mains'.   So I am guessing this will no lnoger work.

Anyone have any thoughts on what we can do to get running?

We have the entire system programmed and running on a test system input (ie function generator) so Im hoping to not lose any time invested in programming.

1. is there is a new product that has the channel to channel isolation?

2. is there a way to maybe do a voltage divider down to the 30V level, which is possible, but not ideal.

3. A way to reference measurments ground to lower potential outside of a voltage divider

4.  Do we even need the channel to channel isolation anyway?

thanks

Jim

[TommyDunkz]

Hi Jim,

NI does offer some cDAQ modules that have channel-to-channel isolation. However, neither of the modules with 32 analog input channels have it. When you say that 12 cells is the minimum, do you mean that you intend to measure the voltage of up to 32 batteries at once? In such a case, I'd take measures to reduce the effect of ghosting, since the channels are multiplexed to one analog-to-digital converter. (see: http://digital.ni.com/public.nsf/allkb/73CB0FB296814E2286256FFD00028DDF)

As for the voltages, the module itself is only designed to read voltages of up to 10V. At higher voltages, you risk losing data resolution and potentially damaging the hardware. So, I would recommend doing the voltage divider if you are dealing with greater than 10V.

[Biosolutions]

hello

thanks for the reply

what modules do offer isolation?

i can do the VDR if need be, that is not difficult.

if we already have working code, will alot of it have to be changed ?

that link you sent about ghosting is giving me an error

would like to read it

yes, we are reading up to 32 cells in series at 4.2v each for some tests we would like to do

Error

HTTP Web Server: Lotus Notes Exception - Entry not found in index

thanks

Jim

[TommyDunkz]

Hi Jim,

Sorry, that URL was including the closing parenthesis I added. This one should work: http://digital.ni.com/public.nsf/allkb/73CB0FB296814E2286256FFD00028DDF

For modules offering channel-to-channel isolation, I would recommend checking out this page, and filtering based on Isolation Type (near the bottom of the column on the left): http://www.ni.com/data-acquisition/

As for your code, do you mean what will change if you switch to a different module?