Our full technical support staff does not monitor this forum. If you need assistance from a member of our staff, please submit your question from the Ask a Question page.


Log in or register to post/reply in the forum.

253 soil matric potential sensor:


zhangyp Aug 17, 2011 07:19 AM

Hello:
I have a doubt about 253 soil potential sensor. I measured 30 each 253 sensors by AM16-32B. My program as follow:

PortSet (7,1 )
PulsePort(8,10000)
BrHalf(kOhms(1),1,mV250,7,Vx1,1,250,True,0,250,1,0)

PulsePort(8,10000)
BrHalf(kOhms(2),1,mV250,7,Vx1,1,250,True,0,250,1,0)

PulsePort(8,10000)
BrHalf(kOhms(3),1,mV250,7,Vx1,1,250,True,0,250,1,0)






PulsePort(8,10000)
BrHalf(kOhms(29),1,mV250,7,Vx1,1,250,True,0,250,1,0)

PulsePort(8,10000)
BrHalf(kOhms(30),1,mV250,7,Vx1,1,250,True,0,250,1,0)

PortSet (7,0)

For j = 1 To 30 Step 1
kOhms(j)=kOhms(j)/(1-kOhms(j))
'Equation for linear (0 to 200 kPa) relationship
WP_kPa(j)=7.407*kOhms(j)/(1-0.018*(T109_C(j)-21))-3.704

Next j

My problem is that when I change the integration parameter to 50Hz, the measure result will bigger than 250us’s result. For example: when use 250us, the result is 16.7, change to 50Hz, the result is 32. I don’t know why, is there any body can help me?


aps Aug 17, 2011 11:29 AM

The 253 sensor requires a fast AC style excitation. If you apply the excitation for a longer period you will start to see polarisation errors, caused mainly by the electrochemical effects on the electrodes of the sensor. The 50 Hz option applies the excitation for approx 40 times longer than the normal recommended fast measurement so this is probably the cause of the errors.

Log in or register to post/reply in the forum.