This is a 4-20mA loop regulation video. This video demonstrate the 4-20mA loop regulation video. In this video, the current is depending only on the pressure that trough the regulation circuit. When there is no pressure, the current still zero, and then when the pressure is applied the current will increase up to 12mA. This current does not depend on the supply voltage. Here is the video:
When the supply voltage is decreased into 15V, the current still 12mA. And When it is decreased more, the current still 12mA. When the supply voltage is 9V, the current change repeatedly, it’s not constant. When the supply is high enough the current is back to 12 mA.