terminal of the ppm transmitter 58 is connected to a transister 64 one example of a preferred transister is a ztx749 the output of the transmitter 64 drives the led emitter diodes 42 and the transmit indicating lamp 38 the other components of the circuit are identified in a conventional manner the transmitter circuit as described above remains in a power down mode until either of the contacts of the first control switch 34 or second control switch 36 are closed by an operator or technician upon release of the first control switch 34 or the second control switch 36 the transmitter circuit returns to its power down mode now referring to fig4 a schematic for the receiver 14 circuit is shown this schematic includes a power supply and control relay section 66 a control logic section 68 and a plurality of infrared sensor and pre amplifier sections 24 the power supply and control relay section 66 interfaces between the power source from the x ray unit and the logic section 68 this section preferably is capable of input power voltage supplies between the range of 9 24 vdc or 7 18 vac the output voltage of this section 66 is 5 vdc this section 66 also includes three individual control relays not shown the three relays are adapted for having their contacts operate in parallel with the prep expose and collimator lamp circuits.