The Sitrans Probe is -as you know- a 2-wire instrument (and it's an excellent one!).
It needs some current to start up. Maybe your analog card does not provide enough power, or your loop resistance is too high. I have seen this many times.
By means of test, connect your Sitrans Probe directly to a 24V power supply (e.g. Sitop Power), and see if it does start up completely. When the start up phase is done, you will hear / feel the pulses on the sensor face.