Many OMRON's relay specify the contact resistance with this:
The contact resistance was measured with 10 mA at 1 VDC with a voltage
drop method.
Such as http://www.omron.com/ecb/products/pdf/en-g6a.pdf.
Then, how the test circuit are arranged? It's apprently 1VDC/10mA is not equal the contact resistance they stated. If we already know the current flow through the contact, then why they specify the voltage '1VDC'? Apparently it's not the voltage drop on the contact. Any special reason?
Best Answer
Relay contacts are often not reliable for very small voltages and currents. 1V @10mA means that a voltage of 1V appear across the relay contact when open and 10mA flows when it is closed. In practice, this could be done more than well enough with a simple 100\$\Omega\$ resistor and a 1.00V source, since the failure level of 50m\$\Omega\$ would represent only 0.05% error (measure the voltage across the closed contact).
10mA and 1V is a relatively easy current and voltage for a relay to switch, at least a relay of this particular type.
The failure rate at low currents is specified as 'P' = 60% confidence of 0.1 failure in 10^6 operations at 10uA/10mV, and that's with the relay clacking away at once per second. Caution is called for if you are operating infrequently at low level currents. This kind of relay is sometimes used in precision instrumentation- and it may make sense to 'exercise' the relays before taking a reading.