What is the current general recommendation for wiring the connection of an RS232 sensor to a CR1000 on a Com1-4 ? I find no recommendations in the manual. Did I miss it?
Should one use a protective connection such as page B-1 of the CR10X manual?
As far as level limiting, see CR1000 manual,
Section 4.8, p.91 :
http://s.campbellsci.com/documents/us/manuals/cr1000.pdf
For 9-pin RS-232 implementation:
Pin 2 (Rx) to Tx on COM1,Com2,Com3,or Com4 of CR1000
(C1, C3, C5, C7)
Pin 3 (Tx) to Rx on COM1,Com2,Com3,or Com4 of CR1000
(C2, C4, C6, C8)
Pin 5 (Gnd) to G on CR1000.
If that doesn't work right off, I would try switching
Pins 2 and 3 (Tx,Rx) around. (DCE vs. DTE, etc.)
Thank you. I was mostly concerned about the level translation and protection.
Yes, I missed that diagram on pg 91. I thought I had looked at every page referenced in the index.
Considering the circuit in the diagram and the text above it, let me attempt to restate what appears to be the case.
The Cx Com pins on the CR1000 are capable of sinking the current normally supplied by a modern RS232 device driving a +12V signal and pulling it down to a +5V neighborhood. These inputs are also capable of sourcing current to pull up a modern RS232 -12V signal to the -0.6V neighborhood. Furthermore, most modern RS232 interfaces operate when driven with 0 to 5V signals even though these levels are not proper per the RS232 specifications.
The effect is that we can customarily directly connect an RS232 device to the CR1000 without additional components and expect it to function and not damage the logger. Not always but almost always.
Is that a correct summary?
The control ports are protected with 500 mW zener diodes and a 220R series resistor which limits the voltage that passes to the internal logic. That circuit will protect the logger from connection to RS232 devices that meet the standards, i.e. have a nominal output impedance of 300R or higher.
Any device that is connected will inevitably be dumping a few mA of current into the logger because of the voltage clamp and this will happen all the timeif the device is outputting a negative voltage in its idle state. To avoid this issue you can add a 10-20K series resistor to the input to limit this current further.
The logger does not have this built in because of the multi-use function of the control port which can source some current when configured as an output.
Thank for the quantitative description of the Cx ports. I wish such information was in the manual or available white papers.
From what I know, the circuit is a very good design considering it's multiple uses.