current meter

[lakeshoretest2005]

Hello community,

In my application, I am using the 4070 DMM current inputs in series with my DUT power. It seems that by default, the current inputs are not conductive.

I realize there is a fuse, but is there also a FET driver or some switch in series with the current meter which can prevent conduction? Is there a circuit diagram somewhere on the ni.com site?

I issue a command to setup the DMM measurement parameters, e.g. scale, resolution, etc., but the DMM does not seem to be conductive until I issue the "get measurement" command. Is this normal operation? Are there other commands that will cause the current meter to conduct? What commands will cause the current meter to be non-conductive?

Thanks, a priori, for any help.

[Teigen]

Hi,

An electromechanical relay is used to to complete the circuit through a high precision shunt resistor when a current measurement is configured. The following is an excerpt from the NI Digital Multimeters Help file>>Devices>>NI 4070>>DMM Measurements>>DC and AC Current.

"Tip The current measurement path within the NI 4070/4072 utilizes an electromechanical relay that provides very low resistance to assure a low burden voltage. While this relay has an exceptionally long life, you can take special precautions to ensure reliable operation.

Whenever possible, switch the NI 4070/4072 into the current measurement function before applying the current. Switching inductive current sources generally creates flyback voltages that stress the relay and, if done frequently, can shorten the reliability of the relay. Also, avoid interrupting the current by switching out of the current measurement function when currents are flowing through the circuit."

To help answer the question on which functions will put the path between the current terminals into a conductive state, I'll need to know which programming language you are using. Please post a reply with this info and I'll be happy to respond with a follow up.

Regards,

Scott Teigen
Applications Engineer
National Instruments

[lakeshoretest2005]

Scott,

Thank you for the help. I am using Labwindows CVI 6.0. Any additional insight you can provide is appreciated.

[lakeshoretest2005]

Scott,

Do you have any further information on putting the current meter into a conductive state? Thanks.

[Teigen]

Two functions can be used for putting the current meter into a conductive state. The niDMM_Initiate and niDMM_Read functions will actually commit the configuration settings in hardware. If you need the the connectors to be conducting current before connecting the DUT, taking a dummy current measurement using the niDMM_Read function will accomplish this.

Regards,

Scott T
Applications Engineer
National Instruments