PFI developed Long Distance TEDS (LDTEDS™) as a method of extending communication distances for TEDS sensors. While traditional TEDS sensors are limited to a distance of 300 feet between the signal conditioner and sensor, LDTEDS can communicate at distances to 1500 feet and beyond. LDTEDS has enabled TEDS sensors to be used for applications such as weapons test or vibration test on large structures where safety, environment, test article size and other factors often require cable runs in excess of 1000 feet.

Some transducers such as piezo-resistive pressure transducers can have very high resonant frequencies that can be excited by transient events and this out-band signal can be larger than the signal of interest. Sources of unwanted low frequency noise can exist such as engine sub-harmonics, triboelectric noise from cable whip or pyro-electric noise from the sensor caused by the large temperature gradients.

The 28000 amplifier gain is distributed as “pre-filter” and “post-filter” gain to allow the filter to remove out-band signals such as transducer resonance while still achieving the required full-scale in-band signal level. Using the 28000 “reserve” feature, the user can specify the required protection against out-band noise and the pre- and post-filter gain are automatically distributed to provide this protection. The pre-filter gain is set to achieve the required amplifier headroom for the out-band signals prior to the filter while maximizing dynamic range. After the filter removes the out-band signals, the post-filter gain is set to achieve the desired full-scale output.

The Precision Filters 28304 and 28324 accelerometer conditioners have built in “T-Insertion” capability to electronically stimulate the attached piezoelectric accelerometer to output a charge signal. The charge output of a stimulated accelerometer is dependent on the exact properties of the accelerometer and connecting cable. And can be used to detect any change resulting from a faulty or damaged accelerometer. Additionally the stimulation frequency can be increased to interrogate the accelerometer in the vicinity of its mounted resonance frequency. Since resonance characteristics are affected by accelerometer mounting, high frequency performance can identify mechanical damage that occurred during a test run.

In summary, T-Insertion can be used as an “Electronic Tap-Test” to gather information on all accelerometer channels quickly and easily from the convenience of the control room. Pre- and post-T-Insert measurements can also be presented as a report that can greatly enhance QA documentation and add a new level of test validity documentation.