WorldViz User Forum - sensors confused

I want to use the sensor of the three.
these sensors want to fixed number[A,B,C], (no value[x,y,z])

for example)

sensorA(fixed number) = (10,10,10) <-x,y,z (receive(change) value)
sensorB(fixed number) = (20,20,20) <-x,y,z (receive(change) value)
sensorC(fixed number) = (30,30,30) <-x,y,z (receive(change) value)

so, i am used this code.

Code:

vrpn = viz.add('vrpn7.dle')

sensorA = vrpn.addTracker('PPT0@166.104.29.228',0)

sensorB = vrpn.addTracker('PPT0@166.104.29.228',1)

sensorC = vrpn.addTracker('PPT0@166.104.29.228',2)



def update(): 

      position1 = sensorA.getPosition()

      position2 = sensorB.getPosition()

      position3 = sensorC.getPosition()

     

      a =  position1[0]

      a1 = position1[1]

      a2 = position1[2]

     

      b = position2[0]

      b1 = position2[1]

      b2 = position2[2]  



      c = position3[0] 

      c1 = position3[1]

      c2 = position3[2]

      

      A = [a,0,a2]

      B = [b,0,b2]

      C = [c,0,c2]

      

      # vector

      v1 = vizmat.VectorToPoint(A,B)

      v2 = vizmat.VectorToPoint(A,C)

      v = vizmat.AngleBetweenVector(v1,v2)

      Forearm.setEuler([0,0,-v])

      UpperArm.setEuler([0, -30, -80]) 



      print v

 

vizact.ontimer(0,update)

but , the sensor's number is frequently change.

for example)

sensorB = (10,10,10)
sensorA = (20,20,20)
sensorC = (30,30,30)
.
.
.
sensorC = (10,10,10)
sensorA = (20,20,20)
sensorB = (30,30,30)
.
.

How do i receive the fixed sensor's number?