Dear all,
I want to measure the battery voltage of my built-in batteries in my control cabinet with the CR1000.
For measuring the 12V resp. 24V voltage of the battery I use a voltage converter, connected between CR1000 and battery.
When I measure the voltage with a voltmeter between the H and L connection (or between H and GND) at the CR1000 I get other results as the datalogger itself is measuring.
In combination with the used multiplier (times 6) the CR1000 shows 20V instead of 24V measured.
My program code lines I was testing the measurement with are
VoltSe (Battery_Voltage,1,mV5000,13,False,200,250,1,0) resp.
VoltDiff (Battery_Voltage,1,mV5000,7,True,200,250,1,0)
Does anybody have an idea?
Thanks for your help.
Best Regards
* Last updated by: trashbk on 7/11/2012 @ 4:22 AM *
What is this converter and how is it wired please?
If I could send you a screenshot via mail this would be the best, but I try to explain
The converter consists of four wires with two implemented resistors (590 kOhm and 110 kOhm).
Batt24V+ is connected to H (of CR1000) via the 590 kOhm resistor R1 (in series); Batt0V is connected to GND (of CR 1000); The second resistor R2 (110 kOhm) is wired in parallel between H and GND.
That should work, with a multiplier in the VoltSe instruction of 6.3636 it should give volts.
A couple of things to watch out for though. With such high value resistors you may need to use a larger settling time than the default - try the 50/60 Hz integration option which has a longer default settling time.
The other potential issue is the risk of problems cause by differences in the ground voltages. If there is any chance the 24V supply has its ground at a different level to the logger you risk measurement errors or even damage by connecting the two grounds together. A differential measurement with dividers to ground on both high and low inputs is safer.
The 50 Hz integration is working better, thanks.
You mean that for differential measurement I should connect my two ends of the converter to H and L of CR1000 whereas L is bridged to GND?
Please have a look at the divider and their connections in this manual:
http://s.campbellsci.com/documents/us/manuals/vdiv.pdf
For testing purposes I take 12V and GND from Datalogger an get 12.23V back with 6.3636 multiplier, even with 50Hz and maximum settling time.
Do you have an idea from where the difference comes from, or is it normal measurement error of CR1000?
Thanks for your help
Best Regards
The measurement error from the logger should only be of the order of 0.1% maximum at room temperature. What tolerance are the resistors you are using?