AM503: Difference between revisions

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AM503 (view source)

Revision as of 01:50, 10 September 2017

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It was requested that we change the design to be a TM500 plug-in module instead.   
It was requested that we change the design to be a TM500 plug-in module instead.   
The AM503 front panel still looks like a scope’s plug-in.   
The AM503 front panel still looks like a scope’s plug-in.   
The AC/DC switch and 5MHz bandwidth switch, for example, were left on the front panel from the oscilloscope design.
The AC/DC switch and 5 MHz bandwidth switch, for example, were left on the front panel from the oscilloscope design.
There are still some remnants of the oscilloscope circuits, such as the [[cam switch]] that interfaced to a circuit board that sets the scope’s readout in amps/div.   
There are still some remnants of the oscilloscope circuits, such as the [[cam switch]] that interfaced to a circuit board that sets the scope’s readout in amps/div.   
The square pin header connector on the back of the circuit board was for the readout, but not used.   
The square pin header connector on the back of the circuit board was for the readout, but not used.   
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The AM503 was also intended to work with future higher frequency probes, like the [[P6022]] with an added hall device for DC measurements.   
The AM503 was also intended to work with future higher frequency probes, like the [[P6022]] with an added hall device for DC measurements.   
The smaller P6022 had a 120 MHz bandwidth, whereas the [[P6302]] was only 50 MHz.   
The smaller P6022 had a 120 MHz bandwidth, whereas the [[P6302]] was only 50 MHz.   
The design engineer (actually only an R&D technician) moved to the TM500 engineering and evaluation group before this probe was created.  
The design engineer (actually only an R&D technician) moved to the TM500 engineering and evaluation group before this probe was created.  
The AM503 was being developed in the Accessories division in Beaverton, since that’s where the other current probes were designed.   
The AM503 was being developed in the Accessories division in Beaverton, since that’s where the other current probes were designed.   
That was unusual as all the other plug-ins were being designed by the TM500 group on Walker Road, near Hillsboro.
That was unusual as all the other plug-ins were being designed by the TM500 group on Walker Road, near Hillsboro.
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There were some innovations that were incorporated in this design:   
There were some innovations that were incorporated in this design:   
The [[cam switch]] with replaceable laser trimmed attenuator resistors, a 1GHz Gilbert cell op amp (actually developed by Howard Jones in 1963).   
The [[cam switch]] with replaceable laser trimmed attenuator resistors, a 1 GHz Gilbert cell op amp (actually developed by Howard Jones in 1963).   
This IC, [[155-0078-xx]], was being developed by Tek’s IC department.   
This IC, [[155-0078-xx]], was being developed by Tek’s IC department.   
(At the same time these IC designers were teaching the technology at the University of Portland as part of Tek’s excellent education and training program.)  
(At the same time these IC designers were teaching the technology at the University of Portland as part of Tek’s excellent education and training program.)  
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The Hall device used for the DC measurements used a vacuum deposition process with indium antimonide.
The Hall device used for the DC measurements used a vacuum deposition process with indium antimonide.
The cores were lapped and polished to a few Fresnel lines flatness to minimize the gap on the sliding ferrite.  
The cores were lapped and polished to a few Fresnel lines flatness to minimize the gap on the sliding ferrite.  
The L/R time constant affects the point where the Hall device and Coils’ bandwidths crossover.
The L/R time constant affects the point where the Hall device and coils’ bandwidths crossover.
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An interesting aspect of the design was trying to find a way to test and calibrate the peak current pulse on the larger P6303.   
An interesting aspect of the design was trying to find a way to test and calibrate the peak current pulse on the larger P6303.   
Luckily we had the tube lab.  We developed an argon filled thyratron that could discharge a 4KV charge line into a 4 ohm load.   
Luckily we had the tube lab.  We developed an argon filled thyratron that could discharge a 4 kV charge line into a 4 Ω load.   
The load resistor was designed and built by Tektronix.  A large rectangular ceramic plate was coated with a metal film resistor.   
The load resistor was designed and built by Tektronix.  A large rectangular ceramic plate was coated with a metal film resistor.   
It had a voltage divider tap to allow for a safer measurement point.  It was laser trimmed for accuracy.
It had a voltage divider tap to allow for a safer measurement point.  It was laser trimmed for accuracy.
The current probe would measure the current to ground through this resistor, so the voltage was near zero for the user.   
The current probe would measure the current to ground through this resistor, so the voltage was near zero for the user.   
The 4KV supply was charged into a 4 ohm transmission line so a clean high current pulse would be generated.   
The 4 kV supply was charged into a 4 Ω transmission line so a clean high current pulse would be generated.   
This concept was taken from Tek’s [[109]] pulse generator.
This concept was taken from Tek’s [[109]] pulse generator.
A trigger circuit was designed to fire the grid.  It was based on the xenon flash circuit of the C5 camera flash, also in the Accessories group.
 
A trigger circuit was designed to fire the grid.  It was based on the xenon flash circuit of the [[C-5|C5 camera]] flash, also in the Accessories group.
The first prototype I made arced across the laser trim lines in the metal film resistor as they were cut perpendicular to the current flow.   
The first prototype I made arced across the laser trim lines in the metal film resistor as they were cut perpendicular to the current flow.   
This caused high voltage gradients across the film and thus the arcing across the cuts.   
This caused high voltage gradients across the film and thus the arcing across the cuts.   
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Also interesting, the P6303 require special potting epoxy developed by 3M.   
Also interesting, the P6303 required special potting epoxy developed by 3M.   
The epoxy used in other current probes put excessive stress on the larger ferrite that caused the inductance to drop to zero.   
The epoxy used in other current probes put excessive stress on the larger ferrite that caused the inductance to drop to zero.   
The magnetostriction property of ferrite.   
due to the magnetostriction property of ferrite.   
The epoxy could even also cause shear fractures in the ferrite.  
The epoxy could even also cause shear fractures in the ferrite.  
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