leitmotif
Member
How does the 4 to 20 mA output of a sensor respond when the measured parameter goes negative.
Example
Hall effect used for current monitor on a battery. When charging let us call that a positive current flow and positive 4 to 20 proportional to 0 to XX amps battery current.
Discharging current is call it negative and 4 to 20 mA would have to be negative.
How would sensor and the "monitor" ie PLC or digital instrument
etc handle the change (transition?) between
+4 and - 4 mA
when current changes from neg to positive?
I would want a "polarized" signal ie positive when current is positive and neg when current is neg.
I do not recall mention of this question
Is 4 to 20 mA a poor choice for this application?
Am I better off with voltage type signal ie mV or 0 to 10??
This is for electric vehicle and I would want to record battery discharge and charge current. Would like 4 to 20 for best EMI "immunity" and to avoid the small negative values seen on voltage signals when measured parameter is at zero.
Another interesting thought
if I monitor shaft RPM to get velocity and distance what happens when I back up?? In PLC of course I could check for a negative value and throw it out or change to a positive but what about a simple digital readout without this capability?
Uhh is this a realistic concern / question or am I doing hand wringing and Chicken Little here?
Dan Bentler
Example
Hall effect used for current monitor on a battery. When charging let us call that a positive current flow and positive 4 to 20 proportional to 0 to XX amps battery current.
Discharging current is call it negative and 4 to 20 mA would have to be negative.
How would sensor and the "monitor" ie PLC or digital instrument
etc handle the change (transition?) between
+4 and - 4 mA
when current changes from neg to positive?
I would want a "polarized" signal ie positive when current is positive and neg when current is neg.
I do not recall mention of this question
Is 4 to 20 mA a poor choice for this application?
Am I better off with voltage type signal ie mV or 0 to 10??
This is for electric vehicle and I would want to record battery discharge and charge current. Would like 4 to 20 for best EMI "immunity" and to avoid the small negative values seen on voltage signals when measured parameter is at zero.
Another interesting thought
if I monitor shaft RPM to get velocity and distance what happens when I back up?? In PLC of course I could check for a negative value and throw it out or change to a positive but what about a simple digital readout without this capability?
Uhh is this a realistic concern / question or am I doing hand wringing and Chicken Little here?
Dan Bentler