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I'm desinging a generic sinking 4-20mA current loop transmitter and I'm trying to find out it it's ok for my output to sit at 0mA when the
microcontroller is off.
The system uses a PWM output to a low pass filter, into a Burr-Brown XTR115U. Due to the speed of the microprocess the minimum current I
get out ( a 1% duty cycle of the PWM) is about 4 mA. I had been using a biasing resistor so that the system was always at 4mA when there was
power on the loop (even if there was no power to the micro).
Is there any reason why I shouldn't allow this system to sit at 0mA when the loop is powered and the mico is off? The world of the 4-20mA
is new to me, and I want to be sure that 0mA shouldn't screw up any of the equipment that might be connected to this device.
- Thomas
microcontroller is off.
The system uses a PWM output to a low pass filter, into a Burr-Brown XTR115U. Due to the speed of the microprocess the minimum current I
get out ( a 1% duty cycle of the PWM) is about 4 mA. I had been using a biasing resistor so that the system was always at 4mA when there was
power on the loop (even if there was no power to the micro).
Is there any reason why I shouldn't allow this system to sit at 0mA when the loop is powered and the mico is off? The world of the 4-20mA
is new to me, and I want to be sure that 0mA shouldn't screw up any of the equipment that might be connected to this device.
- Thomas