The Full Scale Interface section "2.2.2 Power Station Input Signal" defines no lower limit for the power station interface signal. The July 2012 version defines a rejection voltage limit of 4 volts. The limit was removed in the June 18, 2020 draft because 4 volts seems entirely arbitrary, and likely too high to conform to at least some existing product in the market.
However, we should probably have some limit, and the suggestion is that the limit be 1.5V. This is high enough to prevent noise, or other superimposed signals, from being mistakenly interpreted by the Power Station (booster), but low enough that it will still be easily filtered by the input threshold voltage of both opto and digital isolation circuits.
Found in the June 18, 2020 PDF Draft version.
The Full Scale Interface section "2.2.2 Power Station Input Signal" defines no lower limit for the power station interface signal. The July 2012 version defines a rejection voltage limit of 4 volts. The limit was removed in the June 18, 2020 draft because 4 volts seems entirely arbitrary, and likely too high to conform to at least some existing product in the market.
However, we should probably have some limit, and the suggestion is that the limit be 1.5V. This is high enough to prevent noise, or other superimposed signals, from being mistakenly interpreted by the Power Station (booster), but low enough that it will still be easily filtered by the input threshold voltage of both opto and digital isolation circuits.