Instrument for conversion of a standard d.c. current signal into a standard pneumatic signal, for the change-over from electrical controllers to pneumatic control valves, or from electrical measuring system to pneumatic controllers. The PC15 is a force balance device, which converts the input signal 4...20 mA, 0...20 mA or 1...5 V, 0...10 V to a proportional output signal 3...15 psi (0,2...1 bar), 2...20 psi (0,14...2 bar) or 4(6)...30 (0,3...2 bar), with a respective supply pressure of 25 or 45 psi (1,7-3 bar).