Hello All,
I tried to connect a Kipp&Zonen CGR3 (with Thermistor) at an CR5000 but I've problem with the Thermistor.
The manual of CGR3 is lacking in technical information so I read the CNR4 manual of campbell rev11/10: I think the thermistor is the same of CGR3
In Differential mode it propose (I write only the Thermistor wiring):
Thermistor Signal -> single-ended Input
Thermistor Voltage Excitation -> VX
Thermistor Signal Reference -> Analog Ground
Shield -> Ground
The manual suggest:
BrHalf (Vs_Vx,1,mv5000,16,Vx1,1,2500,True ,0,250,1.0,0)
Rs = 1000*(Vs_Vx/(1-Vs_Vx))
cnr4_T_C = 1/(1.0295e-3+2.391e-4*LN(Rs)+1.568e-7*(LN(Rs))^3)-273.15
So in my Program:
'*****************************************************
'*** Kipp&Zonen CGR3 Pyrgeometer
'*****************************************************
'measurements CGR3Dn
'CGR3 Sensitivity 14,74 uV/W/m^2
'Wiring
'ANALOG INPUT
'11H CGR3 - downwelling shortwave radiation signal (red)
'11L CGR3 - downwelling shortwave radiation signal reference (blue)
'GND CGR shield (clear)
'Vx1 CGR3 Thermistor (yellow)
'23 SE CGR3 Thermistor (green)
VoltDiff(T2_CGR3Dn,1,mV20C,11,True,200,250,CNR1_MULT_Sens,CNR1_OFFSET)
BrHalf (Vs_Vx,1,mV5000,23,Vx1,1,2500,True ,0,250,1.0,0)
CGR3_Rs=1000*((Vs_Vx)/(1-Vs_Vx))
CGR3TK=1/(1.0295e-3+2.391e-4*LN(CGR3_Rs)+1.568e-7*(LN(CGR3_Rs))^3)
With this code the Thermistor temperature appears incorrect.
I read some interventions on the forum. These suggest connecting a 1 kohm resistor between SE and AG.
In the CNR4 manual this is not mentioned.
I'm confused... I need the Resistor or there's a mistake in my program?
Thank
Daniele
Daniele
The datalogger measures voltage, a thermistor puts out current, you have to convert the current to a voltage via a resistor. While I do not know the exact setup you have, I used the following to wire up a IR pyranometer to a CR1000 that also had a thermistor:
http://s.campbellsci.com/documents/us/technical-papers/eply-pir.pdf
Hopefully that helps
Thanks joshdr83,
I read more carufully the cnr4's manual and I found:
"Campbell Scientific adds a completion resistor in
the pig tail end of the thermistor cable, so that it is easily interfaced with our
dataloggers for half-bridge measurement."
this is the reason why, in the wiring scheme, the resistor is not mentioned.
my CGR3 is original from Kipp&Zonen, without resitor in cable so I nedd to connect a resistor betwen SE and AG.
Right now are in possession of only a 120 ohm resistor, I suppose, by suitably modifying the code [CGR3_Rs=120*((Vs_Vx)/(1-Vs_Vx))], can be fine until I can get one more suitable.
In doing so, I risk demaging something?
Daniele
I doubt it would hurt anything - but you may want to make sure that the tolerance and temperature coefficient of the resistor are what you want or need. I use a .01% 5ppm resistor for my IR measurements.
So if you're using the CR5000 then why aren't you using an IX instead of a VX? If you pulse a current through your thermistor and measure voltage, won't that work with out having to utilize an extra resistor?
Hi to All,
as described in the user manual of Campbell, CGR3, you must complete the circuit of the thermistor with a 1 Kohm precision resistor and most important, stable in temperature (0.1% accuracy and 10 PPM/C°or minus), otherwise the temperature measured depends by the temperature of the sensor and also the temperature of the datalogger (if the R. 1Kohm is wired near to the terminal block of the logger). For a test, you can use any type of R. 1kOhm, you can find in any electronic-components shop. You can also try to find those type of high accuracy, but it will not be easy. Campbell sells the "Terminal Input Modules" for this, like 4WPB1K. Some online catalogs sells these, in small quantities too, such RS COMPONENTS or FARNELL, but they are only electronic components, and you must arrange a well done wiring for terminals of logger. You may find these type of components, if you are a "Campbell user" in many Campbell sensors, if you have some of it in disuse, such as 107, 108 or others. Campbell often uses these type of resistor in their resistance sensors. With 120 ohms will not can work. Try to read the manuals for the models 107 and 108 and in the section "support".. "document", there is a technical manual that describes how to measure thermistors generic (Technical Note 15-95AS).
There are other posts in the forum where we talk about generic thermistors.
Smile
Also, are you sure that you not have the CGG3 model with a 100 Ohm platinum resistance, this is an request option to for Kipp & Zonen
Smile
The CGR3 we are using includes the thermistor. I ended up using technical note 15-95AS and calculated the appropriate resistance as 11.9K OHM using a half bridge w/ linearised output between -10 degC and 40 degC. So now I'm looking for a precision resistor with temperature stability that's 12K OHM and unfortunately, it's harder than I have expected, but I am getting there. Thank you for all of the help, Smile. You were invaluable.
Best,
Wrangham