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The remainder of this subtopic describes the MAIN_ENERGY circuitry and optics. The SAFETY_ENERGY
circuit operates in the same manner.
A sample (
0.2%) of each YAG pulse is deflected from the first surface of the first (synthetic) sapphire wedge
optic to an imaging mirror. The imaging mirror forms an image of the rod end on the PYRO1 pyrodetector
(located on the Optics Bench PCB). The heat generated by this energy striking the pyrodetector generates a
small current, the integral of which is proportional to the energy in the pulse. This current is amplified by U1
on the Optics Bench PCB and is asserted to the input of the Main Differential Receiver U13-3, which receives
the differential voltage. The signal is sent through the Main Zero Correction circuit U16-2 (this circuit ensures
that the energy monitoring circuit is at a zero level before each pulse). Depending upon the wavelength
selected, the microprocessor will output a signal (MAIN_HOLMIUM or MAIN_NDYAG) by way of the Digital
I/O EPLD U49 to U17 to select the proper gain stage. The energy signal is then asserted to the integrator U14.
U40 outputs a /Q1/ signal to set the integrator and then as the signal is asserted to the Peak/Hold detector
U20. U20 charges to the highest level seen out of the integrator for a given pulse. The /Q1/ signal also sets the
Peak/Hold detector.
U20 outputs a voltage signal (MAIN_ENERGY) to the following areas:
• Analog to Digital converter U31.
The MAIN_ENERGY signal is asserted to the input of the A/D converter U31-19 to be
read by the microprocessor.
• Voltmeter output U26.
The MAIN_ENERGY signal is asserted to the non-inverting side of the amplifier U22-
3. The output becomes the input to U26 which can be read by an external voltmeter.
NOTE: 1 Volt = 1 Joule in Holmium or Nd:YAG
Note that the energy monitoring circuit for the safety detection channel operates exactly the same as the main
energy detection circuit.
The imaging mirror is used to provide a constant image size on the pyrodetector surface for different beam
sizes (the beam cross section tends to be smaller as pump energy increases). This provides a more consistent
energy sampling across the range of pulse energy.
After the value of the MAIN-ENERGY and SAFETY_ENERGY is read, the MAIN_ENERGY and
SAFETY_ENERGY channels must be reset before the next pulse is delivered. To reset the circuit, the Safety
Control Logic EPLD U40 asserts a /Q1/ signal to the following chips:
• U17 in the main energy detection channel.
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