The load on my cct has a maximum current rating of 2.25 amps. The source voltage won't exceed 5.75 volts. I need to monitor the voltage and desire to monitor the current as well. Absolute accuracy is not critical. I am using a DPM that requires resistors be installed per the attached instructions(page 1 for voltage, page 2 for current). I plan to use a DPDT switch to switch the DPM between current and voltage with the output to the DPM connected to the common poles.

Would the attached schematic work(page 3)? The voltage drop across the .1 ohm resistor (A and B) would be used for the current measurement. The voltage would be read across the 100K resistor( C and D).

Thanks

 

This looks perfectly good to me.

Just checking...you do know that "break before make" is critical to make this work, don't you?

 

I am guessing you mean that the meter cannot be connected to both inputs simultaneously? The switch is a mini toggle (On-On). Are On-On toggles generally a no-no in this case? Would an On-Off-On DPDT meet the requirement?

Also as an alternative could I remove power from the meter before switching over or do I have to disconnect the input from the meter?

All of the above is only assuming I really understood your reply. In any case thanks very much for your help.

 

0.1 ohm will give you 225 mV for 2.25 A, which will be out of range. Have you thought about the decimal point switch/jumper? The 20V range will have decimal point switch position 2.

Finally, how are you powering the meter? Are you powering it from the source or will it have a separate power supply, like a battery? Some DPM's allow you to do either, but others will require a separate supply.

John

 

I am guessing you mean that the meter cannot be connected to both inputs simultaneously? The switch is a mini toggle (On-On). Are On-On toggles generally a no-no in this case? Would an On-Off-On DPDT meet the requirement?

That is correct. And a toggle switch like you have will work well. The moving contact will come off the one fixed contact before it contacts the other.

 

thnks to all in all