components as shown trunking 97 forms a channel or conduit for electrical and pneumatic wires and lines further shown are rail 85 and connector blocks 87 to facilitate the interconnection of electrical components the tester 26 further includes digital input output modules 86 the inventor has found three adam 4055 u2122 modules manufactured by advantech u2122 to be suitable for this purpose these modules 86 include an isolated converter to convert rs 232 signals from the controller 36 into isolated rs 4 22 or rs 485 signals without having to change the controller 39 s hardware or software the inventor has identified advantech u2122 model adam 4520 as a suitable unit the embodiment of the tester 26 shown includes two power supplies to power the different components reference numeral 102 refers to a dc power supply unit which is an ac dc switching power supply unit with a single output and remote open sense lead protection features the inventor has found the condor international plus series 24v dc power supply to be suitable in addition reference numeral 94 indicates a primary switched mode power supply unit used in the embodiment shown the inventor has found the phoenix contact 24v dc 2a mini ps 100 240ac 24dc 2 model suitable for this application also included is a safety relay 90 and three solid state relays 88 two applied to isolate a pneumatic system of.