HT-100
Automatic Hole Scanner System

• Portable unit, easy to carry and use on the job site.
• Proven, reliable eddy current circuits.
• Lightweight, hand-held scanner improves test reliability and reduce operator fatigue.
• Scanner provides simultaneous rotation and linear motion of the probe.
• Continuously variable rotational speeds range from 40 to 120 RPM.
• Use with shielded or unshielded probes.
• A wide range of probe sizes are available.
• Built-in chart recorder provides a permanent record of test results.
• Includes a multi-step filter switch to improve signal-to-noise ratio.
• Hole standard test block calibrates and checks equipment performance.
• Convenient case stores scanner, probes and all accessories.

The Model HT-100 Automatic Hole Scanner System is a compact, portable instrument widely used for locating surface and near-surface discontinuities on the interior of fastener holes in metal parts and assemblies. Eddy current testing, proven the most effective method of detecting hole flaws, requires only a minimum of hole surface preparation. Visual and penetrant methods of inspection cannot normally be used, because of metal smear within the hole.

The HT-100 is most commonly used for the detection of fatigue cracks in fastener holes in high stress areas of aluminum parts and structures. It can also be used on materials such as titanium or steel. In most cases, it is possible to detect and identify flaws while still shallow enough to allow oversizing of the hole and installation of a larger fastener. The instrument can also be a valuable fatigue testing tool for crack growth studies on inservice aircraft or other structural members.

The HT-100 Hole Scanner System consists of a portable, easy to transport carrying case housing the eddy current control and readout instrumentation, and a lightweight, hand held scanner. The scanner accepts a wide range of hole inspection probes, both shielded and unshielded, with the most popular sizes being the in range of 3/16" to 1/2". The probe is simultaneously rotated and linearly driven into and out of the hole under the control of a thumb operated rocker switch. Rotational speed is continuously variable from 40 to 120 RPM and the probe linear travel is .025" for each revolution. The scanner also includes a control for setting the probe insertion depth anywhere within the range of 0" to 1-12/".

The case includes all eddy current instrumentation, filter and amplifier circuits, scanner motor control circuits and built-in chart recorder.

The main system controls include:

The built-in chart recorder can be controlled manually or automatically in conjunction with the scanner control switch. It provides a permanent record of the eddy current signals obtained during the scan. Choose either filtered or unfiltered recordings. Five filter settings facilitate finding the best filter to noise ratio. The edge effect is also suppressed, so that cracks at or near the edge of the hole or at an interface can be detected.

The test block contains holes with machined slots on the inside surface. It calibrates and checks probe response. It also sets of the instrument controls, to give the same sensitivity for any probe.

All instrumentation is housed in a fiber glass case with heavy duty latches and handle. The case cover provides cushioned storage.

The HT-100 is easy to calibrate and use. First, set the controls. The probe is then inserted a short distance into the hole and the eddy current test frequency adjusted to obtain lift-off compensation. This is especially important in order to reduce irrelevant indications caused by hole surface roughness or probe wobble. The RPM and filter controls are interrelated. They provide maximum suppression of the effects when a hole is out of roundness, or when there is when surface disfigurement. Using the test block or similar standard, the gain is then adjusted to obtain the desired signal amplitude on the chart recorder (in response to a known defect in the test block hole).

The depth of scan can be adjusted by turning a control at the top of the scanner while viewing the actual setting through a clear window. The scanner, held comfortably in one hand, is controlled simply by thumb operation of the rocker switch. Upon hole entry, scanning and recording is accomplished by setting the switch in the forward position. When the pre-set depth is reached, both probe drive and chart advance will stop. To inspect and record as the probe exits the hole, remove the probe or set the scanner switch to its reverse position.

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