EBM30N/TEG
–
Installation and User Guide
Document Number: 81773-4
Issue: 2
Spellman High Voltage Electronics Limited
|
+44 (0)1798 877000
|
Broomers Park, Pulborough, W. Sussex, UK. RH20 2RY
TEMPLATE: 40776 ISS A | ECN I-10067 | DATE: 16/04/21
QA/ENG/SAL
© 2021 Spellman High Voltage Electronics Corporation
Page 5 of 16
1
Description
The EBM30N/TEG consists of one chassis containing a complete high voltage power supply to power
the main components within a Scanning Electron Microscope (SEM).
The chassis is approximately 105mm x 190mm x 250mm.
1.1 Rated Outputs
Output
Rating
Notes
Accelerator
-30kV, 170µA
Internal Supply. Voltages up to 32kV can be
generated.
Bias Cancellation
3.5kV, 150µA
Internal Supply. Referenced to Accelerator
output.
Bias
N/A
See section 1.2
Filament
15W
max into 1Ω
Referenced to Accelerator output.
P.M.T.
1.3kV, 1mA
Referenced to ground.
Scintillator
11kV, 250 µA
Referenced to ground.
Collector
500V, 5mA
Referenced to ground.
The ‘source’ outputs (
accelerator, bias and filament) are provided at a Claymount mini 75 receptacle.
The P.M.T. and Collector outputs are provided at BNC.HT connectors (Radiall R316 553)
The Scintillator output is provided at a bespoke
‘poke
-
home’ receptacle.
All control and monitoring is by analogue and TTL level signals.
1.2 Bias Output and Bias Cancellation Supply
The Bias Output is not controlled directly: it is referenced to the Accelerator Output and varies with the
load current and the Bias Cancellation Supply as described below.
The negative Bias voltage is generated by the feedback resistor current and the load current flowing
from the accelerator through a 20MΩ +/
-5% resistor to the filament centre tap. See the block diagram in
the next section. The maximum off-load Bias voltage is therefore dependent upon the accelerator
voltage and the 500MOhm feedback resistor as shown in the block diagram.
Beam (emission) current conduction is achieved by cancelling this bias voltage with the positive polarity
Bias Cancellation supply.
An Accelerator output of -30kV will generate a current of -60uA feedback into the 500M feedback
resistor, which is equal to a voltage of -1200V generated across the 20M
Ω
resistor.
So, the Bias sits at -31200V which blocks the flow of electrons. The positive Bias Cancellation voltage
reduces the negative Bias output allowing the emission current to flow.
