How many 4-20mA sensors can connect to CR1000 ?
CR1000 specs:
Analog Inputs: 16 single-ended or
8 differential individually configured
is this pressure sensor(ht-hydrotechnik Pressure Probe type 655) 4-20ma single ended or differential ?
http://www.ht-hydrotechnik.com/cms/front_content.php?idcat=39&lang=2
That is a 2-wire 4-20 mA transmitter, and it could be connected either way, single-ended or differential. E.g., if the same power source is used for the datalogger and for the transmitters, then the current from each transmitter would go through a separate resistor and back to ground, and an SE terminal could measure the voltage at the 'top' of each resistor.
Alternatively, a differential measurement could be made across the resistor for each transmitter, allowing the voltage to 'float', i.e., not be tied to the datalogger's ground. The differential measurement is effectively reading the voltage at both ends of the resistor and reporting the difference.
Care would need to be taken to avoid 'ground loops' if separate power sources are not completely isolated, and also to make sure the common mode voltage does not exceed the capacity of the datalogger.
* Last updated by: kirving on 12/8/2014 @ 12:50 PM *
CSI customers measuring 4-20mA sensors often
use a CURS100 (precision completion resistor), or
they purchase a resistor themselves used in a similar
way to accomplish the current to voltage conversion.
(like kirving described).
http://www.campbellsci.com/curs100
Look at section 4 in the manual here:
http://s.campbellsci.com/documents/us/manuals/curs100.pdf
The ground wire of the sensor is tied to both L (low)
and ground. The other lead goes to H (high).
Using the CURS100, there is only room for 8 (not 16)
sensor inputs. However you do reduce the risk of ground
loop problems
http://s.campbellsci.com/documents/us/product-brochures/b_tims.pdf
Then what i must or can do, to reduce ground loop problems ?
i want to use 10 x 4-20mA sensors.