The Keysight 34461A is the most precise instrument on your bench. This lab teaches its four jobs (DC volts, DC current, resistance, continuity), uses it to check Kirchhoff’s voltage law, and shows two traps every engineer falls into once: plugging into the wrong input, and the meter changing the circuit it measures.
The voltage input (red “Input VΩ HI”) looks like a huge 10 MΩ resistor, so you connect it across a part and it barely disturbs anything. The current input (red “I”, lower right) looks like a near-zero resistance, so you break the circuit and put the meter in series, like a piece of wire. Mixing them up is the classic mistake. Pick a hookup:
Two channels of the power supply are stacked: 1 V on top of 2 V, both “+ up”, driving a 300 Ω resistor. KVL says that if you walk once around a loop, adding voltage rises and subtracting drops, you end up back at 0. Press play to walk the loop.
The DMM shows V(HI) − V(LO). Swap the leads and you measure the same voltage from the other end, so 3 V becomes −3 V. Neither is wrong; the sign tells you which end is higher.
Current has to flow through the meter to be counted. So you open the loop and let the meter close it. Put “I” toward the + of the 1 V supply and “LO” toward the resistor so the reading comes out positive.
The circuit only needs 10 mA. A 100 mA limit means a wiring mistake (like the one in section 1) puts the supply into CC instead of destroying something.
In Ω mode the DMM pushes a small known current through the part and measures the voltage, then divides: R = V/I. In 2-wire mode the same two leads carry the current and sense the voltage, so the leads’ own resistance gets added in. In 4-wire mode a second pair of “sense” leads measures the voltage right at the part while carrying almost no current, so lead resistance drops out.
Skin resistance varies a lot between people and with moisture; these are typical values. Never touch anything above 42 V.
Two 10 MΩ resistors in series across 5 V should split it evenly: 2.5 V each. But the voltmeter is itself a 10 MΩ resistor. When you clip it across one resistor, you put 10 MΩ in parallel with 10 MΩ (5 MΩ), and the divider changes. Toggle between an ideal meter and the real one.
Ω mode in a powered circuit (steps 24–25): the ohmmeter assumes the only voltage it sees is from its own test current. The circuit’s 2.5 V adds to or subtracts from that, so one lead order reads far too high and the other reads near zero or negative. Resistance readings in a powered circuit are meaningless: always turn the power off first.
A divider makes a smaller voltage from a bigger one using two resistors. Enter your pre-lab target and this picks the nearest standard 5% values, then shows the voltage you will actually get. If a value isn’t in the bins, combine two resistors in series or parallel.