See emonTx calibration page for summary of calibration coefficients. 

Different AC to AC power adapters

A 9V AC-AC adapter can be connected to the emonTx to give an AC voltage sample. This can be used to measure the AC RMS voltage which in turn can be used to calculate real power, power factor, frequency and detect power flow direction. 

Not all AC-AC adapter are the same. Variations in design, materials and construction means the output AC waveform varies between different adapters.

MW (UK plug)

Rating: 9V AC 500mA

Primary resistance: 700 ohm

Secondary resistance: 2.4 ohm

Quiescent power consumption: 3.9W

Supplier: ?

Strontronics (UK plug)

Rating: 9V AC 100mA

Primary resistance: 266 ohm

Secondary resistance: 1.3 ohm

Quiescent power consumption: 2.5 - 3.4W

Supplier: Farnell http://uk.farnell.com/stontronics/ac-09100bs2-1/adaptor-9vac-1a-uk-2-1/dp/1279503?Ntt=1279503

Mascot 9580 (UK plug)

Rating: 9V AC 300mA

Primary resistance: 1.37Kohm 

Secondary resistance: 3.3 ohm

Quiescent power consumption: 1.4W

Supplier: RS http://uk.rs-online.com/web/p/products/400-6484/

FP AD 3515 (euro plug)

Rating: 9V AC 528mA

Primary resistance: 970 ohm 

Secondary resistance: 3.5 ohm

Quiescent power consumption: 1.5W

Supplier: RS http://uk.rs-online.com/web/p/products/459-853/

 

TDC

Rating: 9VAC 600mA

Primary resistance: 705 ohm

Secondary resistance: 2.3 ohm

Quiescent power consumption: 0W

Supplier: http://www.idealpower.co.uk/