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Thermocouple psychrometer on CR6 : TCPsyc


DavidCo Sep 29, 2020 06:11 AM

Hello,

I would like to use PST-55 sensors from Wescor (thermocouple psychrometer) with Campbell datalogger.

10 years ago, these Wescor sensors were used with a CR7 with a A3497 and a specific software S3497X.

Today, CR6 and instruction "TCPsyc" allow to use these sensors again. But, i don't understand some points :

- When i use a program with TCPsyc instruction, in results I have a output of 4 values which are "Voltage Offset, Psychrometric depression in uVolts, Estimated Water Potential in MPa (Brown Model), and Sample Temperature in degrees C" but no more explanations, especially on the way water potential is estimated (and i really would like to understand or have the brown model equation).

- It appears I can't use this instruction with a Slowsequence or with a "If Flag".

- how this instruction works, i mean step-by-step ? Is this possible to reproduce this TCPsyc instruction by a sequence of instruction ?

Here the example program used :

'TCPsyc Example

'Declare Variables
Const REPS = 1
Const MeasFreq = 4 'Hz; set by sample option parameter
Const MeasTime =20 'Seconds
Public Meas(4*REPS+(MeasFreq * MeasTime))’use constants to scale array if using output option 1

Alias Meas(1) = Voffset
Alias Meas(2) = uVMax
Alias Meas(3) = Psi
Alias Meas(4) = Amb
Public Tref

BeginProg
  Scan(1,min,0,0)
    PanelTemp (Tref,60)
    TCPsyc(Meas(),REPS,U1,Tref,0,-6000,1,20,2,20) 'sample option 2 = 4 Hz
  NextScan
EndProg

Thank you for helping me !

Davic.C


Notso Oct 5, 2020 05:07 PM

Hi David,

You can download the document with the Brown & Bartos (1982) model at http://www.treesearch.fs.fed.us/pubs/31297. I will send you details on the step by step measurements and calculations that happen in the TCPsyc instruction directly to your email.

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