which SWITCH is made up of double-pole double throw relay

[木虫]

Hi, I'd like to know that which SWITCH in NI is made up of double-pole and double-throw (DPDT) relay? Because DPDT has very small thermal EMF.

On the other hand, if I increase the aperture time of the 4071 (7 1/2) whether I could get more accuracy?  

Thanks in advance.

[EricS.]

National Instruments does not currenly offer any switch modules that have DPDT relays.  However, if you are looking for low thermal EMF, the PXI-2503 offers <2uV of thermal EMF.

Yes, you can also increase the aperture time of the 4071, which would give a more accurate overall measurement by reducing the impact of noise, but that measurement would still include the thermal constant thermal EMF across the relays.

[EricS.]

I should clarify: NI does not currently offer any switch modules with DPDT topologies, exposing all of the pins of a DPDT to the user.  However many of our modules do use DPDT relays internally to create other topologies.

[木虫]

Hi,Eric,

    Thanks for your reply.

    Now i have anther question: Whether the FET relay is suitable for transfer small potential? 

     Thanks!

[木虫]

Hi, Eric,

  I'd like to know that whether the 12uV EMF of 2569 is the worst case (It has more channels). By the way, whether the electromechanical relay in 2503 is SPST? 

  Thanks.

[木虫]

Hi, Eric,

    Another question comes. i'd like to know that which SWITCH is made up of DPST?

    Thanks for your reply.

[EricS.]

To answer your questions in order:

1. Are FETs suitable for small potentials?

How small of a potential do you want to switch?  FETs usually have slightly higher offset voltages (usualy still under tens of uV) than electromechanical EMF voltages.  If you are trying to switch uV signals then this would be a problem, but if you are above a few mV potential it would probably be negligible. 

2. Is the12uV EMF of 2569 is the worst case?

Yes.

3. Is the electromechanical relay in 2503 SPST? 

No, the 2503 uses DPDT relays.

4. Which NI switches use DPST?

None of NI's switches use DPST.

If you want to see the hardware diagrams you can always view the rough layout in the NI Switches Help. Under the Devices book you will see a list of all of NI's switch product line.  Each will have an associated topic "Hardware Diagram" that you can use to view the relay types and how they are connected.  In all cases where you see what looks like a DPST it is actually a DPDT without the last throw connected.  You can also look at the "Relay Replacement" topic to see which particular relay is used on that device and get more information from the relay manufacturer.

[木虫]

Thank you a lot!