Multiple 2602b SMU LabVIEW (GPIB)

Hello everyone, 
I have three 2602b SMU in a setup. Each one is used for applying a voltage sweep and measuring a drop in current. The triggering and processing of information is done through LabVIEW. All the SMU are connected via GPIB in series. If only one SMU is active the sweep is continuous until it finds the drop in current, but if two or the three are activated they take turns receiving and sending information. The problem is that they make the whole process slow. I'm not trying to do simultaneous trigger. They have to work independently and not stop in any moment until it meets the condition. 
Is there any way to make them work continuous and independently through the same connection? 
Sorry for the bad grammar English is not my first language.
Thanks. 

Hello,
Please elaborate on the sweep until it finds a drop in current.  Is the sweep implemented as a loop controlled from LabVIEW?  And the LV code is where the evaluation about current drop occurs?
 

Hello,

Yes, the sweep is in a loop. The trigger and buffer reading are in different VI. In the buffer reading VI we subtract the previous reading with the recent reading to know when there is a difference in current. It's like a contact from a relay. The contact is in a certain distance and by rotating a screw the distance closes or opens. The contact has to close with 24 mA applied. We apply various sweeps since a stepper motor si doing the calibration by moving the screw. This is done by three stations at the same time continuously but the three power supply are being controlled by one PC through GPIB.