having had a quick look at the AKZ250 manual
this is what you have when the sensors NPN open collector output is connected to one of the AKZ250 inputs
I have calculated the additional resistance required to limit the AKZ250 input current to 7mA when you connect it to a +24V supply
the pull up resistor I calculated is 2700 ohms
the value given in the manual is 3300 ohms this will reduce the current that will flow into the AKZ250 input
and will reduce the voltage you will measure at the AKZ250 input terminal to about 4.64V
when the sensor is triggered and its NPN output transistor short circuits the AKZ250 input to ground
the voltage at the input terminal will depend on saturation voltage of the NPN transistor -
the 0.7V you have measured is what I would expect
as the sensor has a normally open NPN open collector outputs that only sinks current to GND and can not supply current from the 24V supply
it is safe to connect sensors in parallel
the AKZ250 will only sense when the first sensor is triggered
I expect you will need to set the sensor as active low in mach 3
as the AKZ250 input is high (+5v ) until the sensor is triggered and the AKZ250 input goes low (0.7V)
John