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I've been involved in a few projects with HVAC systems, where sensors etc. generally used 0-10 V signals, and looking at catalogues of Buderus and other suppliers this still appears to be the standard.

In other industrial applications, you typically see 4-20 mA for analogous signals. When checking the Endress & Hauser catalogue at random, some sensors aren't even available with 0-10V signals.

Why this discrepancy?

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I don't have a clear picture regarding HVAC, however I've used a lot of sensors both current and Voltage in many industrial and academic environments and projects.

To my understanding current sensing is less susceptible to noise. I.e. you can transfer signal to greater distances without loss. Additionally, the 4-20mA has the added benefit that you can "sense" if something is wrong (e.g. a wire has broken off). Its also probably slightly more expensive than voltage sensing.

The drawback, is that voltage sensing is more probably more intuitive, potentially requires less power intensive, and finally and more probably more importantly, there are a lot of voltage sensing peripherals. As a matter of fact, in many cases where you have a device that outputs a current, what you do is you connect a Resistor , close the circuit and measure the voltage across the resistor.

For industrial applications and noisy environments, 4-20mA makes a lot of sense.

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Both 4-20mA and 0-10V (0-5V) are used in process control. 

The 4 to 20 mA current loop is series, low impedance, long distance (>20m), noise resistant, two-wire, typically point-to-point, break or not connected detection (0mA), susceptible to increased series terminal resistance, and low rate of change sensors.

The current loop can be multi-point, but in it's simplest form, tranducer (transmitter) drives current based on actual line resistance, and receiver uses resistance to turn measurement into voltage. 

4-20 mA is harder to measure during troubleshooting because meter has to inserted in series or clamp-on meter must clamp onto one wire of twisted pair wire. 

The 0 to 10V voltage protocol is parallel, high impedance (low current A/D converters), short distance (<50m), prone to electrical noise and interference, multi-point, three-wire (seperate power supply), no break or open circuit detection (0V could be signal or open), less susceptible to parallel terminal resistance, easier to measure (voltmeter in parallel) and understand and troubleshoot (5V = 50% vs 12mA, 12-4 = 8/16 = 50%), fast rate of change sensors, and voltage drop over long wires causes different readings at different stations.

From Analog Circuits Training - Understanding Analog Circuits 0-10VDC 4-20mA:

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Although 4-20mA are usually used for really long sensors, both can be used for all applications.  Main difference is voltage is usually used for quick response sensors like motor control, and current loops for slower changing sensors, like pressure and temperature. 

Why one company prefers one type or the other, comes down to preferred expertise of designers and typical application. 

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