TOF-MS Voltage Controller

The Kore TOF-MS Voltage Controller contains modules to address four tasks:

1. A high voltage supply provides the excitation for an electron multiplier type detector. The output voltage, for driving a multiplier, is adjustable from 0 to 2.5kV via a front panel ten turn potentiometer. The supply can be floated to facilitate arrangements where modest post acceleration of ions is employed, or where other considerations require the detector first dynode voltage to be independent of the multiplier excitation. Two low voltage signal inputs are available to enable or disable the detector excitation. These can be used, for example, to provide computer control and interlock protection for the detector.
2. Two general purpose high voltage resistor chains are intended to allow one power supply to be used to drive several electrodes in the spectrometer, whilst still allowing independent adjustment. Each chain accepts an input of up to ±5 kV which is applied to the top and is available as an output. A further four lower voltage taps are provided on each chain, each having an associated front panel ten turn dial potentiometer. The boards are designed so that the tappings may be readily moved to anywhere between the top of the chain and earth, with the potentiometer providing approximately 6% of adjustment for fine control. The two chains are completely independent so that one may be operated with the opposite polarity from the other, which is often useful in practice.
3. A set of four high voltage, normally open relays are provided, with their coils wired as two pairs and driven by a polarity changeover input. The high voltage contacts are connected to four high voltage BNC connectors which allow a swapping of connections according to the polarity input. The most typical use for these would be to automatically swap the polarity of a pair of high voltages when changing between positive and negative ion detection. However, they may be used for any purpose compatible with the voltage rating. A pair of low voltage output BNCs are also provided with contact closures that follow the polarity input state. These could be used for additional external relays if required, or to slave the control of some other external unit.
4. Finally there are two +5V supply sockets available, intended for driving external modules, perhaps extra relays or high voltage CMOS switch modules.

TOF-MS High Voltage Supplies

These are the high performance, high stability voltage supplies that are required to perform TOF-MS. The stability of the mass peaks in a TOF-MS is dependent upon the stability of the voltages from the basic supplies to the control unit and out to the instrument, and so we specify high-end supplies, with different current capabilities depending upon the usage.

Kore high voltage supplies

Where a customer does not require a programmable, general-purpose (transportable) high voltage supply, or where the budget makes constraints, Kore can supply dedicated rack-mounted high performance supply modules. The voltage supply performance is equivalent, but there is no front panel control or external computer control capability. The supplies are dedicated and are therefore less expensive.

If there is only one high voltage supply required, we can fit this into the TOF-MS Voltage Controller, meaning that an instrument can be controlled from a single 3U supply. This would be the case, for instance, in an electron ionisation TOF, where positive ion detection is the only mode, and thus only one polarity (negative voltage) is required throughout the spectrometer.

Where two or more high voltage supplies are required, these are located into a separate, 19″ rack-mounted Kore box.

Third Party Supplies (Stanford Research Systems)

Although Kore designs and manufactures high voltage power supply unit, there are occasions where a client would prefer to use a third party power supply units. We have previously integrated third party power supplies such as those by Stanford Research Systems (SRS) into our instrumentation, fitting an SRS-approved modification to allow them to be shut off by a signal from a suitable vacuum gauge controller. They can be rack-mounted along with other Kore 19″ units, or can be free-standing. We are happy to accommodate your preferred power supply unit to create your ideal custom instrument.

TOF-MS Logic Controller

The TOF-MS Logic Controller is particularly useful when building systems where both simple manual control and computer control is required. There are two modules:

1. A logic board provides a central place from which to control the enabling of the system high voltages and the polarity of all supplies. The logic includes a simple timing sequence in response to a request for polarity changeover that disables the high voltages, pauses, changes the polarity, pauses, and re-enables the high voltages. Thus in a manual system, the polarity of the whole spectrometer may be changed with a single switch. Similarly all high voltages can be disabled from a single point, which simplifies safe operation and protection of the system from vacuum accident or other events that require interlocks. If the system is to be computer controlled, then in principle the computer could be made responsible for controlling each high voltage unit separately and for the polarity changeover sequence. However, many designers still prefer to have safety interlocks implemented in hardware , particularly whist software is still under development. And in any case by centralising the high voltage and polarity control the computer interface need consist only of two TTL signals.
2. A second board provides drive for an octopole set of deflector electrodes, such as those provided in the Kore extraction optics. Control is either via front panel potentiometers or via analogue inputs at the back panel. Two sets of front panel controls are provided, the appropriate pair being selected by means of a polarity signal from the polarity control board.

There are a total of eight 9 pin miniature ‘D’ type plugs provided to output polarity and high voltage enable control to other units in the system. Although they each have specific labels and are wired as described below, it is important to realise that the intent of the design is that these can be used for general purposes. Each of the two logical signals, high voltage enable/disable and negative/positive polarity, has been assigned three double pole changeover relays on the internal PCB.

The normally open and normally closed contacts can be easily patched to ground or +5 Volts, or indeed anything else that seems appropriate. External supplies might have a range of conventions for switching polarity or for high voltage enable. For example TTL signal levels, the shorting of a connection to ground or the making of a link. The idea is that any of these conventions can be accommodated by a suitable wiring of one of the sets of relay contacts.

Mains Distribution Box

Kore designed this 19″ rack unit as very useful addition to an instrument rack when the instrument is required to have a single emergency off button that will shut power instantly to all the various other instrument modules. The unit also has a mains power failsafe, meaning that on power failure, the unit remains off until switched on manually. The mains distribution unit can also be fitted with a bakeout timer and supply, and this is seen below in the front panel graphic of the unit.

We have also customised this unit, for instance to close the backing line valves of a diffusion pump system in the event of power failure, to prevent unintentional venting. This unit has front panel, manual ‘on’ switches for re- opening these valves. This is an example of the customisation that Kore is willing and able to do to provide the correct functionality for an instrument.