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You have to check the max/min loads for your equipment which sources the 4-20mA signal.
I read this type of signals from Infrared flame detectors or IR-gasdetectors which can source up to 500 Ohms max.
A new feature in this are HART devices which uses the same wires for a 485 like data transmission to a handheld interrogator.
If you like to use this protocol then the load resistor should not be less then 250 Ohms.
I really don't think a load resistor of 1 Ohm is desired for industrial type of equipment.
First of all: what equipment do you have?
Datasheets? Describe your application a bit more. We really like to help, but we only can help if you provide us with good description of what you need.
Generally spoken the load resistors for 0-20mA devices are around 200-500 Ohms.
If you like to read the value with an analogue input of a PIC then Use a 200 Ohms 1% resistor for load. Normally spoken these devices have an overrange and max source of 25mA. In this setup you can read 0-5V at the input of the PIC. Use some protection circuit if interfacing field wiring.