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Added some information about the vacuum system
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= Vacuum System =
The Vacuum system of the EM9 series is fully automated, and is mostly protected against user operating error. Though one should take note not to change vacuum states while the servo motor controlling the Spool valve is Operation, as this may cause its fuse to trip.
== Automation ==
The EM9 series uses an interesting design of vacuum automation in the form of a Servo Motor Controlled Spool / Pipe valve system. This Servomotor is controlled by means of micro switches and relays. Mode selection is performed by 3 buttons located to the lower right of the console, depressing one of these will trigger a Thyratron Valve (Model RS1), which then delivers power to a mode relay. This then actuates the Servo motor to move the valve spoon into the correct position, based on the measured vacuum.
== Pumping Scheme ==
Pumping wise, the EM9 uses a simple low component count high vacuum system. This consists of a Leybold Oil Diffusion pump and a rotory vain Roughing pump. Valving is accomplished by means of a large Spool valve located above the Diffusion pump, which in tern is located immediately behind the Column Assembly. Additionally a solenoid Valve is used to connect the Exhaust of the Diffusion pump to the Roughing pump, when not evacuating the column, as well a second such valve being used to vent the column for maintenance.
Evacuation of the column is performed by first disconnecting the roughing pump from the diffusion pump exhaust, which simultaneously is isolated from the column by means of the spool valve. The column is then roughed to a pressure low enough for the diffusion pump to take over and evacuate it to a high vacuum. According to the manual, this should take 10 minutes or less, else the diffusion pumps oil my be compromised, as its vacuum is not being maintained by the roughing pump. According to a friend of the author, evacuating the column from ambient air pressure to a roughing vacuum can take up to 2 hours, though the author has not experimentally verified this. In the case this is correct, evacuating the column from Atmospheric pressure to a rough vacuum, would require the user to unplug the diffusion pump before it is allowed to heat up, else the pumping fluid may be ruind.
One interesting note on the vacuum systems design, is the means by which the specimen is placed into the high vacuum of the column. Unlike many newer models, such as the [[EM10]] series, the airlock dose not feature a roughing scheme, but instead traps a volume of 1cm³ around the tip of the specimen exchange rod, which is then vented into the high vacuum of the column. This spike in pressure is then dealt with by the diffusion pump, and a high vacuum is then restored.
This also necessitates that the user shut off the Accelerating voltage and Filament prior to sample exchange. A automated system is present to prevent the user from introducing the large gas load with the filament and high voltage active, but this system is not fool proof, thus it is advisable to manually shut these off prior to specemin exchange.
== Vacuum Gauges ==
The EM9 series features a very simplistic means of vacuum gauging, only featuring a pirani gauge head at the roughing pump line. For safeguarding of the diffusion pump, a membrane vacuum switch is used to prevent the diffusion pumps heating without propper roughing vacuum.
It is interesting to note, that the Pirani Gauge is only Operation when the microscopes automatic vacuum system is set to mode 1 or 2, in the standby / off state of 0, the gauge amplifiers are switched off, and the galvanometer dose not indicate the present vacuum.
== Sealing Scheme ==
Sealing in the EM9 series is heavily reliant on Rod Seals, thus allowing the movement of the spool valve spool as well as connecting pipes to the column. The column proper uses mostly O-Rings for sealing, and dose not feature clamping mechanism to apply pressure to the seals, instead relying on the pressure difference between the columns interior and exterior for the force needed to seal the o-rings. Initial sealing force is applied by the mass of the column segments alone, thus it is possible to lift these segments without undoing any bolts when the column is at atmospheric pressure.
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= Documentation =
= Documentation =
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