SC24 Magnetic Field Cancelling System
Electron microscopes have to operate in an ambient magnetic field comprising the earth’s field and fields radiated by electric power networks and electrical machines. When the ambient field changes, the electron beam in the microscope is deflected, causing loss of resolution and image distortion. The SC24 system stabilises the field by dynamically creating nearly equal and opposite field changes, so that the microscope performance is much improved.
Manufacturer
Spicer Consulting
Spicer Consulting has built a world-wide reputation in magnetic field cancelling for electron microscopes and similar instruments. Today, working with equipment manufacturers and users alike, the company is recognised as an industry expert in maximising the performance of electron microscopes, electron beam lithography systems, CD-SEM and focused ion beam tools. Spicer Consulting magnetic field cancelling systems protect sensitive equipment in the world's leading laboratories, universities and semiconductor manufacturing plants, as well as in the test facilities of electron and ion beam equipment manufacturers. Its magnetic field, vibration and acoustic analysis systems have been adopted as standard equipment for the conduct of site surveys by leading equipment manufacturers.
Key Features
- Makes the ambient magnetic field “OK” for the electron microscope
- Adapts to field changes within 100 μs
- Touch screen intelligent user interface with automatic setup and DC reset
- Simultaneous AC & DC field display with choice of Tesla or Gauss units
- Mixes dual sensors to create virtual sensor “inside” the EM column
- Use AC sensors for cancelling 50/ 60 Hz AC line fields or:
- Use DC sensors for cancelling tram and train DC fields and 50/60Hz
- Built-in test field generator
- Ethernet and USB ports for remote operation and monitoring
Overview
Electron microscopes have to operate in an ambient magnetic field comprising the earth’s field and fields radiated by electric power networks and electrical machines.
When the ambient field changes, the electron beam in the microscope is deflected, causing loss of resolution and image distortion. The SC24 system stabilises the field by dynamically creating nearly equal and opposite field changes, so microscope performance is much improved. The SC24 system comprises a magnetic field control unit, one or two magnetic field sensors and three orthogonal axis multicore cables, that are installed in the room where the field is to be cancelled.
Three power amplifiers in the control unit drive currents through the cables to create a field of the opposite sign to the change in ambient field. The magnetic field sensor measures the resulting field and real time negative feedback reduces the ambient field by the loop gain of the system. The system is dynamic, automatically responding to field changes within 100 μs.
Touch Screen Display
The SC24 user interface is a touch screen LCD display panel shown below. This is a typical display for an SC24 with one or two wideband DC sensors when the system is cancelling and the field is OK. The five buttons control operation of the system. The “units” button calls up the units sub menu to select RMS or pk-pk, Tesla or Gauss units. The choice of units has no effect on cancelling.
The reset button clears the “trip” indicators and resets the “zero field” operating point of the DC sensors. The “cancel/standby” button turns cancelling on and off. Magnetic field amplitudes are displayed with 100pT (1.0 μGauss) resolution. The DC field amplitudes are not displayed for AC sensors.
Adjustment Menu
The “adjust” button enables entry to the adjustment menu (for expert users), typical display in Fig. 2. It also gives the option to “lock” the touch screen and reset the Ethernet password. When the screen is “locked” the five buttons are replaced by a new button that allows unlocking if pressed for five seconds.
The “Mixer”, “Auto Reset”, “Field Generator” and “Trip Level” touch buttons control the adjustments.
Product range
SC22 Magnetic Field Cancelling System
SC24 Magnetic Field Cancelling System
SC26 Magnetic Field Cancelling System
Installation Options
Installation for TEMs and new Lab Builds
This is the design with the best performance that is recommended for large TEMs and for all new-build microscope labs. The multi-core cables each make one turn and are shown in red, green and blue. The actual cables are black or grey and usually installed in white plastic conduits. Where the room has a false ceiling, parts of the cables may be installed above it. The lower parts of the X & Y cables are shown buried below the floor. This is practical for new-build labs. Parts of the bottom Z cable also need to be buried at door openings. Burying the X & Y cables below the floor is recommended for a TEM with a Gatan Imaging Filter for good cancelling at GIF height. For existing microscope installations where burying cables is not an option, the bottom sections of the cables can be at floor level and covered with suitable cable protectors. The X and Y cancelling performance at GIF height will be compromised.
Basic Installation for TEMs and SEMs
This is the second best cable installation. It has been used with Spicer Consulting Cancelling systems since the SC07 model was launched in 1991. It works best if the X & Y cables cross over directly above the microscope column. It requires cables on the floor covered with suitable cable protectors.
Minimal Installation for SEMs
This is the simplest, lowest cost installation. It usually does not require cables on the floor. The dynamic range and the cancelled volume are smaller because the cables are farther from the column. This installation makes larger fields in the adjacent rooms which may not be acceptable. There are many installations of this type on Scanning Electron Microscopes. SEMs. have small columns so can tolerate the small cancelled volume. Their installations are typically “tuned” by adjusting the sensor position to find the sweet spot for best image improvement.
Sensor SC24/DC+AC
With Sensor SC24/DC+AC” the SC24 provides useful cancelling from DC to 5kHz. The cancelling factor is greater than 400 at DC and 100 at 60Hz. The sensor contains small Helmholtz coils that surround its field sensing elements. They are used to offset the DC component of the ambient field including the earths field. At reset, the microcomputer in the sensor adjusts and remembers the currents in the coils to set the X, Y, Z sensor outputs to zero. The reset process takes 1 second. The sensor must be reset if it is moved. Responds to DC so a change in DC field that overloads the cancelling system requires a sensor reset to restart operation at the new ambient field level.
Sensor SC24/AC
With Sensor AC24/AC the SC24 provides useful cancelling from 2.5Hz to 5kHz. The ratio of the ambient field to the cancelled field is called the cancelling factor. It is a function of frequency and is greater than 50 at 60Hz. Adjusts to the new DC level automatically but the transient may overload it for several seconds. There may be image position drift until the sensor adjusts.
Column Sensor Mount
This sensor mount supports a Spicer Consulting magnetic field sensor. It is designed to hold the sensor to the column of a scanning electron microscope (SEM). The two pillars are fixed to the column with cable ties. The sensor is held onto the mount with elastic bands.
SEM Sensor Mount
This sensor mount supports a Spicer Consulting magnetic field sensor. It is designed to raise the sensor above the chamber or loading area of a scanning electron microscope (SEM). It has 3 alternative tubes to adjust the sensor height and a base with three levelling adjustments to enable the pole to be held vertical and stable.
TEM Sensor Mount
This sensor mount supports a Spicer Consulting magnetic field sensor. It is designed to be tall enough to hold the sensor near the specimen stage of a large transmission electron microscope (TEM). It has a heavy base with three levelling adjustments to enable the tough plastic pole to be held vertical and stable. The sensor height may be adjusted by sliding the sensor mount up or down. An extension pole is included, which may be use to increase the height of the mount if required.Downloads
If you would like to learn more about Magnetic Field Cancelling Systems, contact our experienced technical team today. We would be happy to help you find the right solution for your needs. Contact us today!