Spellman EBM20N-5-24 High Voltage Power Supply User Guide
SAFETY
DANGER HIGH VOLTAGE RISK OF ELECTROCUTION
Observe extreme caution when working with this equipment
- High voltage power supplies must always be connected to protective earth.
- Do not touch connections unless equipment is turned off and the capacitance of both the load and power supply are grounded.
- Allow adequate time for discharge of internal capacitance of the power supply.
- Do not ground yourself or work under wet or damp conditions.
Servicing Safety
- Maintenance may require removing the Instrument cover with the power on.
- Servicing should only be done by qualified personnel aware of the hazards.
- If in doubt, return to supplier for servicing.
Description
The EBM20N/5/24 series is a range of 20kV electron gun power supplies designed to drive a Thermionic Scanning Electron Microscope gun with a tungsten filament, it comes in a 5 watt versions. It contains an accelerator power supply, filament supply and bias supply all independently controlled via an analog interface. Refer to appendix 1 for a block diagram of the unit. The unit is powered from a 24V supply, all input connections are via JST single in line connectors. The HV outputs are via a bespoke 3-pole output connector.
Unit ratings
| Output | EBM20N5 |
| Accelerator | 20kV, 250µA (i) |
| Bias | 1.5kV, 150µA (ii) |
| Filament | 12W max into 1.33Ω (ii) |
Notes:
- voltages up to 25kV can be generated
- referenced to Accelerator output
Bias Operation
The Bias HV output is generated by the feedback resistor current and the load current flowing from the accelerator through a 10MΩ resistor to the filament center tap. See the block diagram in Appendix 1. The maximum off-load Bias voltage is therefore dependent upon the accelerator voltage and the 500MΩ feedback resistor as shown in the block diagram. Beam current conduction is achieved by cancelling this bias voltage with the positive polarity HV generator.
An Accelerator output of 20kV will generate a current of 40uA feedback into the 500M feedback resistor, which is equal to a voltage of 400V generated across the 10MΩ resistor. So the Bias sits at -20400V which blocks the flow of electrons. A positive voltage on the Bias reduces the HV and allows current to flow.
Environmental conditions
- Operating temperature: +5°C to +40°C
- Relative humidity rating: 20% to 85% (non-condensing)
- Altitude: Up to 2000m above mean sea level
Safety
- The HV outputs are provided at a 3 pin bespoke connector. The unit must be terminated safely before operation. Hazardous voltages will be exposed if the connector is removed whilst the unit is enabled. The Earth stud of the unit is a protective earth and must be connected to the earth of the system.
- The unit must be switched off for at least one minute before disconnecting the HV connector or removing the access panel.
- The HV outputs of the unit are hazardous and the conditions of this manual must be complied with to maintain safety. Operating the unit in a manner not specified in this manual may impair the protection against electric shock provided by the unit.
Meaning of Symbols
|
SYMBOL |
MEANING |
|
|
Refer to manual before operating |
| |
Caution, possibility of electric shock |
 |
Protective conductor terminal (PE) |
Regulatory Approvals
The unit is designed to meet the requirements of EN 61010-1, UL 61010-1 and CAN/CSA22.2 No. 61010-1. Please consult the factory for further approval information.
Installation of the HV Unit
Mechanical Installation
The EBM20N/5/24 must be secured in position using the M4 mounting holes provided (see section 5 for details). A safety interlock should be used to prevent access to the unit when it is operating. The EBM20N/5/24 consists of one chassis containing the high voltage power supply. The chassis is 270mm X 200mm X 60mm.
Please see mechanical outline drawing below:
Mass:
- 4.4Kg
Electrical Installation
The EBM20N/5/24 is designed for operation from a double insulated or SELV 24Vdc (±5%) supply, the maximum continuous current requirement is 1.5A.
The unit is contained in an earthed case. The earth stud of the unit shall be properly bonded to the main protective earth termination in the end product. The unit should only be used in a Pollution Degree 2 Installation Category II environment.
Consideration should be given to conduct the following tests with the power supply
installed in the end product :
- Dielectric withstand test, between live parts of the power supply and the end product chassis.
- Permissible Limits Test with the power supply installed in the end product.
- Temperatures on power electronics components, transformer windings and accessible surfaces.
The input and output connectors are not intended as field connections and should only be connected to internal wiring in the end use equipment.
The unit is intended for use as a component and no surface of the unit should be accessible in the end product.
Note: Failure to comply with the above could compromise the safe operation of the unit and invalidate the warranty
Connections
Input Power Connector
JHA2, type JST Model B 3PS-VH
| Pin Number | Signal |
| 1 | +24V |
| 2 | 0V |
| 3 | Case ground |
Pins 2 and 3 internally connected together
Signal I/O Connector
JHA3, type JST Model S10B-EH
| Pin Number |
Signal |
| 1 | Filament program |
| 2 | Ground |
| 3 | Bias program |
| 4 | Ground |
| 5 | Accelerator program |
| 6 | Ground |
| 7 | Emission current monitor |
| 8 | Ground |
| 9 | Accelerator monitor |
| 10 | Ground |
High Voltage Output
The HV output connector is a bespoke 3 pin receptacle which mates with a Spellman HV cable assembly. The cable can be supplied as shown in appendix 2, contact your local Spellman HV sales office quoting part number HVC30/3IS/LL1650.
See diagram below for connection details:
Operation of the HV Unit
Control Inputs
The EBM20N/5/24 unit is controlled by analogue inputs using the signal I/O connector shown in Section 3.3.2
The following table details the action of each control signal
| Input Signal | Voltage |
Control |
| Accelerator Program Voltage | 0 to 10V | This corresponds to 0kV to -20kV output (i) |
| Bias Program Voltage | 0 to 10V | Corresponds to 0 to 1.5kV Bias output |
| Filament Program Voltage | 0 to 10V | Corresponds to 0 to 4V Filament output |
Notes:
- Program accuracy only guaranteed above 500V
Monitor Outputs
The EBM20N/5/24 unit is monitored by analogue outputs using the signal I/O connector shown in Section 3.3.2
The following table details the action of each monitor signal.
| Output Monitor | Voltage | Control |
| Accelerator Current Monitor | 0 to 5V | This corresponds to 0 to 255mA output current Including the feedback current (i) |
| Accelerator Voltage Monitor | 0 to 5V | Corresponds to 0kV to -20kV output (ii) |
Notes:
- Limited to 12V maximum.
- Accuracy +/-3% of FS
Appendix 1: HV Unit Block Diagram
Appendix 2 : HV Cable Assembly
Documents / Resources
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Spellman EBM20N-5-24 High Voltage Power Supply [pdf] User Guide EBM20N-5-24 High Voltage Power Supply, EBM20N-5-24, High Voltage Power Supply |
