Amazon.com: Digital Counter, Easy Connection NPN PNP Signal Input Stable Electric Counters Auto Detection for Industrial Control : Industrial & Scientific
TRI-TRONICS RSRC-1 M12 Pigtail Quick Disconnect, Clear Object Sensing, NPN & PNP OUTPUTS, 5-PIN, PHOTOELECTRIC Sensor, RETROSMART, 24 V DC, RETROREFLECTIVE, 6 INCH Range Distance: Amazon.com: Industrial & Scientific
Amazon.com: Water Level Sensor, XKC-Y26-NPN/PNP Non Contact Liquid Level Sensor Switch/Water Level Controller/Water Level Gauge(XKC-Y26-NPN 24V) : Industrial & Scientific