MTS Series LX Laser Extensometer - Manual (Page 38)

LX Laser Extensometer
Monitoring the Reflection Pulses
Operation 38
Monitoring the Reflection Pulses
Connecting an oscilloscope to the Signal Output BNC connector allows the
reflection signal to be monitored. This is very handy during setup or
troubleshooting, especially when checking for spurious reflections from the
specimen.
Set the oscilloscope controls as follows:
• Time Base = 1 msec per division
• Amplitude = 2 V per division
• Trigger = Positive Slope
Adjust the oscilloscope trigger level until there are two pulses of 5 V amplitude
with sharp edges and flat tops; see
“Reflection Pulses” below. Any additional
pulses indicate the presence of spurious reflections which must be identified and
eliminated for proper operation of the instrument.
Spurious reflections usually result from scanning orthogonally to shiny, flat
surfaces. These reflections can typically be eliminated by rotating the offending
surface a small amount (
≈5° to 10°) about the axis of the scan line; see
“Scan
Line Orientation on Specimen” on page 32.
Reflection Pulses
Reflection from
Target #2
Reflection from
Target #1
Normal reflection pulses viewed
on the oscilloscope at the Signal
Output jack on the control panel.
Spurious reflection pulse
viewed on the oscilloscope
at the Signal Output jack on
the control panel.
Direction of
Elongation
Front View
Target #2
edge
Target #1
edge
Specimen
Scan Line