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Product |
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Thermal 2 Head |
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Machines affected |
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All devices with a TH2 head
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Before you start |
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- Note that the head does not generate any humidity-related error messages. If the humidity in the head is too high the head will continue to function until it fails (due to, for example, an electrical short).
- In order to check the humidity inside a TH2 head, the head must have Head Control Board revision D or higher.
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Procedure |
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- Verify the revision of the board. Type the following command at the TH2 prompt (in Splot or Service Shell):
TH2 > ver
Project: Thermal 2
Firmware: 1.01f Release
Build: 1780
Date: Mar 20 2002 15:00:59
Control board: 4
Xilinx: 30
*** Command Success ***
Note: Control board number 4 = revision D, board number 3 = revision C, board number 2 = revision B, and so on.
If the revision of the board is 3 or less, you will not be able to follow this procedure. Escalate to your regional PSS.
- Measure the humidity of the head. Type the following command at the TH2 prompt (in Splot or Service Shell):
Note: Humidity is given as a voltage.
TH2 > volt
+40V 39.72 Volts
+5V 4.93 Volts
+3.3V 3.31 Volts
-5V -4.89 Volts
Vpp 0.00 Volts
+15V 14.90 Volts
Humidity 1.34 Volts
*** Command Success ***
- Convert the value from Volts to a humidity level (relative humidity) using the following formula:
Relative Humidity = [32.258 * Humidity (in Volts)] - 25.806 (at 25° Celsius)
For example, using the voltage measurement from the sample above:
RH = [32.258 * 1.34]-25.806 = 17.42 %
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Interpreting the Results |
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Inside a TH2 head there are two separate cavities:
- An optic cavity, containing the laser and associated imaging optics
- A cooled electronics cavity, containing the head power supplies and controller
Each of these areas has specific environmental limitations:
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Humidity Control |
Risk Assessment |
| Optic Cavity |
- Has an airtight seal
- Is actively desiccated
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Assuming proper functionality of the air supply and internal Nafion dryer, the head is generally immune to external humidity during normal operation. The only humidity-based risk in the optic cavity is long term migration of water vapor into the optic cavity while the head is powered off or in storage.
Note: If the head is stored in very hot and humid conditions (such as 80%RH and 30°C) for over a week, then the head should be purged for several hours before the write laser is turned on. To purge the head:
- Hook up the head, including air lines.
- Turn on the system.
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| Electronics Cavity |
- Has a dust tight seal
- Is actively desiccated
- It is cooled by a passive heat exchanger
Note: The head's humidity sensor is mounted in this cavity.
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- If the system uses a passive chiller, there is no condensation risk as long as the ambient room air is non-condensing.
- If the system uses an active chiller, there is a condensation risk only if the Nafion drying system fails.
The exact safe Relative Humidity (RH) limit is dependent on the chiller temperature. As a guideline, for chiller temperatures between 25°C and 32.5°C, the maximum allowable measured RH in the board box is ~45%
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Summary |
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- If the head has been exposed to very high humidity conditions (80% at 30°C) for over a week, then the head should be purged for several hours before the write laser is turned on.
- For passively cooled systems, there is no humidity-related danger that can be avoided by monitoring the head's humidity sensor.
- For actively cooled systems, the reported RH should be less than 45%RH while the chiller is operating.
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Technical contact |
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Doug Jeffery |
Submitted by |
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Date submitted |
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16 Dec 2003 |
