inputs 34 a 34 34 b 34 34 c 34 and 34 d 34 in fig1 b on the other hand the adaptor plugs adp1 and adp2 are shown configured so that the actuator will operate when either element connected to input 34 a 34 or 34 b 34 is shaded provided either or both of the elements connected to input 34 c 34 and 34 d 34 are lighted or if both of the elements connected to inputs 34 c 34 and 34 d 34 are lighted in fig1 c on the other hand the adaptor pulgs adp1 and adp2 are shown configured to operate the actuator based on the state of the photoelectric element connected to input 34 c 34 regardless of the states of the other photoelectric elements connected to inputs 34 a 34 34 b 34 and 34 d 34 and depending upon the timing signals provided by the multivibrator circuit with the adaptor plug arrangement of fig1 c the actuator operates when the element connected to input 34 c 34 is shaded when the actuator operation signal provided with the adaptor plug adp2 configured as shown in fig1 a and 15b is too short to provide the necessary actuator operation e g reliable rejection of the improperly oriented part the adaptor plug adp2 configured as shown in fig1 d may be substituted for that shown in fig1 a and 15b so that the actuator operation period may be lengthened in field operation the duration of the actuator operation period can be controlled.