January StudentZone Quiz Solution

Question:

Can you apply current division to obtain I1 and I2 for the circuit shown below? Explain briefly.

Try with various resistors 470 Ω, 1 KΩ, 4.7 KΩ. and 1.5 KΩ

When performing the Lab activity - how to connect the ADALM1000? 

 

Feel free to post your approach here so we could discuss.

 

For your reference see the Analog Dialogue Student Zone articles explaining the Source Measurement Unit (SMU) ADALM1000.

What is a Source Measurement Unit or SMU?

  • I used Delta to star transformation to obtain overall resistance of the circuit which I get as R. Now to obtain  I1,I2, either voltage or total current is needed. I'm trying to get the current value as a whole number.

    •  Analog Employees 
    on Feb 3, 2018 8:06 PM

    There are a couple of ways to connect the ALM1000 to this circuit to measure the currents and voltages. The first thing to do is use channel A in source current mode as current source Is as we see here:

    We can set CA to source various currents. The voltage at the output of CA will also be measured and we can use CB as a volt meter to measure the voltages at the other two circuit nodes as indicated by the green arrows.The ALICE meter - source tool is used. Here we have selected CA to source current equal to 4.5 mA. CB is connected to measure the voltage at the bottom of the 4.7K resistor.

    We can obtain the voltage across all the resistors by subtracting the different node voltages and dividing by the resistor value.

    Another way to connect the ALM1000 is to use CB as an ammeter to measure the current flowing in either of the 1K resistors to ground as shown next. Here we have disconnected the upper 1K resistor from ground and connected it to CB.

    If we turn on CB as a voltage source set to 0.0 V ( same as ground ) we have the same voltage conditions but CB will measure the current. Now we are measuring the current flowing into ground from the 1K resistor, Note the voltage at CB is zero. It will be a negative number because it flows away from the resistor and into ground.

    We can similarly measure the current in the other 1K resistor by simply swapping the GND and CB connections.

    Doug

  • What about an answer to the first question ("How well did the measured outputs and calculated outputs compare? Explain any differences"). I found the measured values to be lower than the calculated values but don't have an explanation.
    When performing the same measurements with two multimeters, I found that the measured values are almost the same as the calculated values, so the explanation should be somewhere in the difference between a SMU and multimeter?

    (although this StudentZone is from beginning 2018, I still find it intereseting, hope you can answer!)

    •  Analog Employees 
    on Mar 20, 2021 2:32 PM in reply to MartijnSc

    Has your M1k been calibrated? If you are using the Revision C version (6 pin analog I/O connector) it is probably not since these boards were not calibrated in the factory. If you have a newer board with the 8 pin analog I/O connector, Revision F, then it was factory calibrated and should be accurate to about  1mV.