 They were the industry standard for many decades until the advent of discrete electronic controllers and distributed control systems.With these controllers, a pneumatic industry signalling standard of was established, which had an elevated zero to ensure devices were working within their linear characteristic and represented the control range of 0-100%.In the 1950s, when high gain electronic amplifiers became cheap and reliable, electronic PID controllers became popular, and the pneumatic standard was emulated by 10-50 mA and 4–20 mA current loop signals (the latter became the industry standard).