Agilent Technologies 5517B Operation And Service Manual page 70

8-27. The High Voltage Power Supply (HVPS) requires +15 Vdc as input. This supply generates up to 12 kilovolts
DC at power-on. After the laser emission starts, the power supply output drops to approximately 1.2 kilovolts DC.
8-33. The heater coil is used both to heat the rod and to sense its temperature. For 2.56 seconds (nominal) out of
every 25.6 seconds (nominal) of the warmup cycle (see Figure 8-5), the state machine disables the power amplifier
and the heater allowing the heater coil to stabilize to the rod temperature. The heater coil and a resistor (A3R9
located in the power amplifier section) form a voltage divider. As the heater resistance increases with rising
temperature, the divider voltage increases. The difference between this voltage and the reference voltage is
amplified to provide the warmup mode error signal.
8-34. At the end of the 2.56 second disable period, the heater coil temperature has settled to the rod temperature.
The error signal is sampled and held and the power amplifier is enabled. During the remainder of the 25.6 second
period, the power amplifier, re-enabled and under control of the sampled error signal, drives the heater.
8-35. When the error signal gets close to zero, the warmup error amplifier sends a digital signal called HEATER OK
(HTR OK) to the state machine. HTR OK is sampled by the state machine whenever the error signal is sampled.
After HTR OK is sampled true, the state machine waits 100 seconds before switching to optical mode.
Figure 8-4. Feedback Loop During Warmup
Mode
HP5517B Service
70-5