Can I upgrade my 4421A-10-XX-X to read 2 sensors?

Yes - the 4421A can be upgraded and does not need to be a full replacement, however, this must be performed at the factor by the Bird Service Center.

• Only the 4421A-10-xx-x and 4421A-20-00-0 can be upgraded to offer broader functionality.
• Neither the 4421A-10-xx-x nor 4421A-20-xx-x can be upgraded to include support and functionality for the USB-based pulse sensors. Only the 4421A-12-11-1 presently works with the USB sensors. 

More information about the 4421A meter and its manual can be found using the link below.

4421A Multifunction Power Meter