Rectifier diodes block the flow of current in one direction, working much like a check valve would in a water flow system.
This type of diode is useful in converting AC to DC because it will only allow current to enter in one direction, and the current continues to flow through it to the output side of the diode. You would no longer get the "alternating current" in the output circuit because now the current is flowing in one direction only (DC).
Rectifier Diode Test
Step 1- Set the multimeter to the diode setting.
Set your digital multimeter to the diode setting , which is usually part of the Ohms (resistance) section on the meter. Note: If you are using an analog meter, then set it to the lowest Ohms Ω setting.
Step 2- Disconnect one side of the diode.
Disconnect at least one side of the diode if it is still in the circuit. This will isolate the diode from the rest of the circuit and allow proper measurement.
Step 3- Test resistance across the diode.
Check resistance across the diode. Now check again but swap your leads to the opposite side they were on for the first reading. If you get an open (meter doesn't move) one way, but some kind of reading the other way, then the diode is functioning properly. If you get some amount of resistance both ways, then the diode is shorted. If you get an open (no movement) both ways, then the diode is open.
A typical rectifier diode