diode resistance checks?

[new guy]

I have a bunch of 48volt dc relays. There is a diode connected in parelell with the coil terminals. (the diode can be easily removed for testing). I tested the diode with a Fluke meter on ohmeter test-autorange- in one direction it measures OL in the other direction it measures 2.3 M ohms. I always thought diodes were supposed to measure OL in one direction and LOW resistance in the other? I tested 6 more brand new (in the box) relays, and their diodes read the same thing. Why so high in the one direction you would expect to see low. Are there special diodes that this would be normal? All the diodes were disconnected from the relays when testing. These relays are used in elevator controls.

[josmith]

Resistance readings on a diode depend more on the meter than the diode. Getting consistant readings on known good parts is the best you can do.
The diode check feature gives you go/no go and often tells you the forward voltage of the part.

[Chris Smith]

Your supposed to set the meter to the diode checker setting. It uses a higher current/voltage to test the diode.

Semi Conductor means its semi connected, not completely blocked or completely on.

Diode leakage and diode resistance is never absolute, its partial.

[Dean Huster]

With a digital or analog multimeter, the lower the resistance range, the lower the resistance reading of the diode will be in the forward direction. As the ranges lower, the current used to "measure" the resistance increases, which causes an apparent decrease in diode forward resistance.

Digital multimeters with the "diode" function are displaying the forward voltage drop of the diode with whatever current they are supplying. In addition, they are using a higher applied voltage to insure that most diodes will conduct in the forward direction while the normal resistance ranges may not supply a high-enough voltage, a characteristic that is brand/model dependent.

Dean