4 analogue signals A/D converter Z-4AI-D allows to acquire up to N.4 analogue inputs (ma or V) through a PLC with only digital input/output. The PLC interface is based on three PNP-type signals suited for connection to most PLCs available in the market. The interface is composed of a CLOCK signal generated by the PLC (transistor output), a DATA signal and STROBE signal generated by the module.