When test data, especially pressure test data, in rotating systems are being acquired, the data, at least for turbomachines and especially gas turbine engines, generally must be transmitted to an external location.  For this purpose, various known means are employed. 
In one known arrangement, compressed air lines connected to a pneumatic test point selector switch are separately sealed with axially offset O-rings. 
Any sealing effect achieved by the use of O-rings has the disadvantage, however, that the seal is suitable only for low rotational speeds and particularly for speeds below 6000 rpm.  O-rings are subject to wear and their useful lives are relatively short particularly at high speeds.  Designs of this type also require that the shaft end be readily accessible. 
Additionally, the test data may be adversely affected by temperature conditions. 
In another known solution the test signals are transmitted via slip rings and pressure sensors rotating on the rotor shaft.  The useful life of this equipment is disadvantageously short as the slip rings are subject to wear in service.  Again, the shaft end must be readily accessible.