Hi,
I want to connect a couple of TA/RH-sensors to a Volt-module. TA - Pt100, RH - VDiff. Wiring looks like this (12V and grouding come in addition)
1H - TA_sensor1_H
1L - TA_sensor1_L
G - G_sensor1
2H - RH_sensor1_H
2L - RH_sensor1_L
G - G_sensor1
X1 - X_sensor1, X_sensor2
3H - TA_sensor2_H
asf.
I do not have any problems with the differential measurements, and measuring a single Pt100 with the next sensor not connected is also completely fine. The instructions i use for a single sensor:
CDM_Resistance (VOLT116,1,TA_raw(1),1,mV5000,1,X1,1,2500,True,True,0,50,0.01,0)
PRTCalc (TA_calc,1,TA_raw,1,1.0,0)
Trouble starts when I want to excite two sensors from the same port. I have read the CRBasic Editor help regarding MeasPEx. I understand that I should connect the Pt100s in series, so I put TA_sensor1_L into 3H and jumpered 3L to the ground. That did not do the trick. I got raw values that were exactly half of what I expected. I got the same values without moving TA_sensor1_L and jumpering 3L. At roomtemperature, this works:
CDM_Resistance (VOLT116,1,TA_raw(1),1,mV5000,2,X1,1,2500,True,True,0,50,0.02,0)
CDM_Resistance (VOLT116,1,TA_raw(2),3,mV5000,2,X1,1,2500,True,True,0,50,0.02,0)
PRTCalc (TA_calc,1,TA_raw,1,1.0,0)
My questions are
- is changing the multiplier a viable solution? Probably not, bc non-linear relationships?
- what is the correct way to do the serial wiring in my case?
Thank you very much!
H
With current excitation, you need to wire the PT100 in series to be able to share an excitation channel.
Look at appendix D1 of the 43347 manual for an example.The 43347 is a PT1000, but is measured much like a PT100.
Thank you very much! It works following that example.