dmm current mode

[Damir]

Hello,

my DUT is powered from DC power supply and I need to measure DC current once during test, but my DMM(4072) must be in current mode during several minutes test.

Can I switch DMM to current mode by default at poweup (I want to manually perform COM test using terminal etc. and need DUT powered over DMM by default)?

Damir

[Albert.Geven]

why not? It is born as an instrument, and should perform that job, no voting.

[Makoto]

What measurement mode (voltmeter, ammeter, ohm-meter, etc) shall be applied at instrument start up is very specific to the model. So you need contact the instrument manufacturer.

[Brandon_G.]

Hi Damir,

The 4072 DMM has a default power up state of DC volts.  This was chosen because this is considered the safest operating mode for the DUT and the DMM.  In DC voltage mode the probes are in a high impedance state and will impact the DUT the least.  If we are in ohms mode for example, we are supplying a test current to the probes which will flow into your DUT and could cause unexpected behavior. With current measurements, you are essentially shorting out your probes, which if improperly connected can blow the fuse of the DMM.

Currently, there is not a way to allow you to change the default power-up state of the DMM.  Can you give me a little bit more background on your test setup?  Is it possible to set your DMM to DC current mode first and then switch on your DC power supply?  

Thanks!

Brandon G

[Damir]

Dear Brandon,

my solution is to build a simple startup app, initialising DMM, setting current mode and commit using niDMM Control vi. I'll pass instrument handle with help of global variable to my test app.

Need to test it tomorow, but it should work. I agree default input shouldn't be current. Perhaps DMM's should have independent input for voltage and current. You could measure current and voltage (and power) alternately without reconnect-mux wires. But there is hardly enough place on front panel of DMM... 

Another question. I use 8 SMU-s for testing rechargable batteries. SMU-s are draining batteries in power off/inactive state with few milliamps. Annoying - after the limit criteria is reached or inactive, SMU should completly disconect from battery. The solution is to set active drain current to few uA and to do so rigt after startup. But it takes care...

Thanks for relevant answer.

Damir

[Brandon_G.]

Hi Damir,

Regarding your SMUs, depending on what device you are using, you can do one of the following to minimize or set the current to 0

1.  Use the Output Connected Property Node (4154 and 4132), to disconnet output using relay on the SMU

2.  Leave the output enabled but set the current to 0 (4141/4140)

3. Leave the output enabled but set the current range to the smallest and then set your limit to its minimum (usually 2% of range) (4130).

I hope this help!

Brandon G

[Damir]

Hi Brandon,

my SMUs are 4130 and I solved problem just as you suggested. First time using 4130 I scrached my had trying to set 0 current to pause draining battery. Reading manuals and specs helps :). One small problem persists if PXI is not powered (rare situation). Obviously there is no relay on 4130 output to completly disconect circuitry from DUT?

Damir

[Brandon_G.]

Hi Damir,

The 4130 will sink some current when powered off if the DUT is sourcing current, such as a battery.  This will be in the neigborhood of a few mAs but will depend somewhat on the voltage of your DUT.  If you plan to only sink current into your battery, you can place a diode in series with your DUT to allow the current to flow in one direction and then use remote sense across your DUT to null out the voltage drop you will see across the diode.  

Cheers!

Brandon G 

[Damir]

Brandon,

in most cases I have rechargeable batteries, so diode is no good. If customer will find necessary I will add external relay - I have some free digital outputs. 

BR

Damir