Hi,
in the AM16-32 multiplexer specification the number of operation is expected to be 5 x 10e7. How to interpret this number?
I am using the multiplexer every 5 seconds. It means that i have to expect a mean life time of about 8 years before failing for one channel?
Thanks,
Luis Gonzalez Sotelino
Your sums are correct. However, you need to realise that:
a) it is a mean life time so you may expect a few individual relays to fail earlier, perhaps by up to a couple of years.
b) that figure is actually the mechanical life, i.e. up until the point they stop switching. This is quoted as we expect the relay to be used for very low current, low voltage switching.
c) the contact resistance of mechanical relays increases with the number of switches. So you will see this increase often almost linearly with switching cycles. The electrical life of the relay is usually defined as some point where the resistance gets too high to switch the rated current (this is nominally 2x10e7 for this relay). Generally this is not a limitation for switching signals unless you use the relay in part of a circuit where the contact resistance needs to be low.
If you are switching high currents or there are electrical surges coming down the cables into the relay then the contact resistance will increase faster and the life may be shorter than quoted above.
* Last updated by: aps on 5/23/2014 @ 8:29 AM *
Thanks for the information.
We are using the multiplexer for several Pt100 measurements set up as 4-wires half bridges. So the resistance should be stay "low". Do you have values for the resistance increase? This would allow us to estimate what is the mean life for our application according to the accuracy we want to achieve.
Thanks,
Luis Gonzalez Sotelino
If you are doing 4-wire measurements then the contact resistance of the relay should not really affect the measurement at all as the logger essentially measures the current flowing through the sensor using a reference resistor and the voltage measurement across the sensor is made in a circuit where no current flows.
If you are interested though the spec of the relays, in as much as is published, is here:
http://pewa.panasonic.com/assets/pcsd/catalog/tx-s-catalog.pdf
The contact resistance is measured with a high current flowing though which is not representative of the use of the AM16/32. Furthermore in recent years we have used relays with the special low current contact material for which no data is given.