Pull-down connexion scheme for 9411 pulse measurements

[SimonML]

Hello all,

I am trying to count pulses with the 9411 module from OMEGA reed switch flowmeters  (see attached:FTB8000B). I have also attached my current connexion scheme to do my measurements. My problem is that my flowmeters are not connected to the 9411 COM(they only hate 2 wires) and so the signal is 5V when the switch is closed and 1.5V when the switch is open (never goes under 0.8V). For this reason, the 9411 always stays in ON state and does not count any pulses. I know that the 1.5 V between DIa and COm is normal when the measuring instrument is not driving the signal http://digital.ni.com/public.nsf/allkb/4F03111FABD946348625775A006CFF7C . On this link it says that I need to add a pull-up/ pull-down resistor in my measurements setup (I suppose that it is a pull-down resistor in my case).

I am not really used to this kind of measurements so I hope that somebody could explain to me how I can use a pull-down resistor to ajust my signal in order to measure my pulses ?

Thank you in advance for your answers.

[Dennis_Knutson]

Connect a pillow pulldown to gnd will cause the input to detect a logic zero when the switch is open and s logic one when it's closed. You can also do the opposite by connecting one side to gnd and the other to a pullup to +5.

For the value, the exercise for the student is to calculate it based on the max current for the device.