Miscellaneous Drawings

Varian Ion Pump Controller Overload Protection, EL-1027

Schematic: schematics/GENERAL/EL-1027B.sch.pdf
Page last updated: May 14, 2002

The Varian Ion Pump Controllers have no built-in current overload protection. This circuit provides that function by sensing pump current and removing 120VAC from the controller if an overload is detected. The circuit has under gone many revisions since it was first designed in 1984. This document applies to the version that is current as of 1/1/1999.

Simplified Schematic

The controller circuit itself is modified at three points and a PC board is added to provide control and monitoring functions. The first controller mod is to interrupt the AC to the controller after the fuse with a relay, which provides a means of turning off the controller in the event of an overload. The second modification places a third switch wafer on the meter range switch to provide feedback as to switch position. The third is to place a 10 ohm current sensing resistor in the current return path of the high voltage supply.

The current sensing resistor is inserted between the ground-return tap on the high voltage transformer (pin 5) and the ‘B’ wiper of the rotary switch. The value of the resister is small enough to not affect the ion pump current but large enough to develop a usable voltage. This voltage is differentially sensed by op-amp U1. The amplified output goes both to a second op-amp and a transistor relay driver. The function of the relay driver is to hold the relay energized as long as the controller current is low enough that the ion pump is in no danger of overheating. If the current rises too far, T1 is turned on which turns off T2 releasing the relay. The relay interrupts the AC voltage to the controller preventing a sustained overload. The second op-amp, U2, supplies an isolated, amplified voltage proportional to the current sensed by the 10 ohm resistor which can be monitored by a remote device. The amplification of U1 is set to cause the relay to drop out at approximately 3.5mA; far more than an ion pump should draw in normal operation but well within the abilities of the controller.

A dual polarity 15 volt power supply is needed to operate the PC board. Since the power supply is connected to the AC following the relay and the initial condition of the relay is open, the PC board is not powered at first. A "start/reset" pushbutton is provided to close the relay after the controller power switch is turned on. It is also used to restart the controller after a current overload has shut it down. In either case, the switch must be held down until ion pump current drops below the 3.5mA trip point and the relay energizes. In order to use the controller from a remote position, a pair of wires connected in parallel with the switch is brought from the switch to a 14 pin connector.

The position of the meter range switch has some effect on the current sensed by the 10 ohm resistor. To maintain consistent current readings by the remote device, it is important to know that the switch is in the same position for each reading. The third switch wafer provides a closure only when the switch is in the "5KV" position enabling to remote device to know when readings are valid.

The connector on the back panel provides for remote monitoring & operation functions. A 4 pin connector was added to allow HIRES to monitor the on/off state of the power and to monitor the ion pump current. For ESI & DEIMOS, a 14 pin connector replaced the 4 pin and carries same functions as the 4 pin connector and additionally provides for remote pushbutton operation and range switch position sensing. Only one of these connectors will be used since if the 14 pin connector is used, the 4 pin would be redundant.


Varion Ion Pump Controller, EL-1270

Schematic: schematics/GENERAL/Ionpump.sch.pdf
Page last updated: May 14, 2002

The controller schematic is shown here for reference.