thereto radar transmitter 28 and radar receiver 29 are connected with an electronic evaluation unit 36 to which is connected an evaluation monitor 30 the transmitting antenna of radar transmitter 29 transmits a sharply bundled signal short high frequency pulse of about 2 u03bcs if this signal impinges on a foreign body 26 in a fiber bale 2 a return pulse echo is initiated which returns to radar receiver 29 echo the foreign body 26 marked by the echo is made visible on the screen of monitor 30 as shown at 26a the radar system operates for example in the microwave range fig7 shows a hard pressed fiber bale 2 onto which a sound generator including for example a quartz crystal for generating ultrasonic waves has been placed short sound surges pulses are transmitted into fiber bale 2 pulse generator 32 acts on transmitting quartz crystal 31 as well as on receiving amplifier 33 the pulse given to transmitting quartz crystal 31 becomes visible on the screen 34 of a cathode ray oscillograph on the other hand during periods of inactivity transmitting quartz crystal 31 can operate as a sound receiver in the rest periods between pulses the pulse switched into fiber bale 2 partially impinges on a foreign body 26 and partially on the opposite wall 2b is reflected by both and received again by quartz crystal 31 transmitted pulse a echo b from foreign body 26 and counterwall echo c from wall 2b are shown on screen 34 according to fig8 outrigger 7 of a bale opener e g a blendomat and detacher 7a are provided above fiber bales 2 an inductive slide rod 35 is fastened to the side of outrigger 7 and is provided with a plurality of inductive switches 36 e g bero switches which.