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AM503: Difference between revisions
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The AM503 was a redesign of the [[P6042|6042]] current probe from 1967. | The AM503 was a redesign of the [[P6042|6042]] current probe from 1967. | ||
It was initially going to be an oscilloscope plug-in. | It was initially going to be an oscilloscope plug-in. | ||
About 80% through the project design a new line of products was started called TM500. | About 80% through the project design a new line of products was started called [[TM500]]. | ||
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 5 MHz 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. | ||
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The high frequency amplifier was differential to accommodate an oscilloscope’s differential input. | The high frequency amplifier was differential to accommodate an oscilloscope’s differential input. | ||
The last change was the output stage that was added to convert the differential circuit to single ended, and then output that to a front panel BNC. | The last change was the output stage that was added to convert the differential circuit to single ended, and then output that to a front panel BNC. | ||
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. | ||
The AM503 was one of the first plug-ins for the TM500 line of products. | The AM503 was one of the first plug-ins for the TM500 line of products. | ||
It required more power than the current plug-in designs so the transformer and supply were changed in the TM500 frames early on just for the AM503. | It required more power than the current plug-in designs, so the transformer and supply were changed in the TM500 frames early on just for the AM503. | ||
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, and a simple IC with a differential pair plus 1 GHz Gilbert cell (actually developed by Howard Jones in 1963). | The [[cam switch]] with replaceable laser trimmed attenuator resistors, and a simple IC with a differential pair plus 1 GHz Gilbert cell (actually developed by Howard Jones in 1963). | ||
This IC, [[155-0078-xx]], was designed in Lab Scopes for the 485. | This IC, [[155-0078-xx]], was designed in Lab Scopes for the 485. | ||
(At the same time designers were teaching amplifier technology internally and at the University of Portland as part of Tek’s excellent education and training program.) | (At the same time designers were teaching amplifier technology internally and at the University of Portland as part of Tek’s excellent education and training program.) | ||
The [[Peltola connector]], developed by Tek’s Ron Peltola, | The [[Peltola connector]], developed by Tek’s Ron Peltola, a very low cost connector that worked well, even for the highest frequencies. | ||
A BNC was adapted to be used with the Peltola and is used on the front panel. | A BNC was adapted to be used with the Peltola and is used on the front panel. | ||
A large section of the AM503 was basically duplicating the front end of an oscilloscope since that was the original design intent, | A large section of the AM503 was basically duplicating the front end of an oscilloscope since that was the original design intent, | ||
so it was thought later that the differential amp section could be eliminated and the amplifier made much smaller and even become part of a standalone probe. | so it was thought later that the differential amp section could be eliminated and the amplifier made much smaller and even become part of a standalone probe. | ||
A prototype was created (author’s senior project at the University of Portland) but shelved, as there was no longer an engineer in Accessories for current probes. | A prototype was created (author’s senior project at the University of Portland) but shelved, as there was no longer an engineer in Accessories for current probes. | ||
Much later it gave rise to the TCP series of stand-alone current probes. | Much later it gave rise to the TCP series of stand-alone current probes. | ||
The [[P6302]] and [[P6303]] probes utilized a Hall device that was manufactured in the clean room of the Accessories Manufacturing group. | The [[P6302]] and [[P6303]] probes utilized a Hall device that was manufactured in the clean room of the Accessories Manufacturing group. | ||
It was deposited onto a bar of ferrite that was later assembled into a U shape with other ferrite and potted in a mu-metal can along with the transformer bobbins. | It was deposited onto a bar of ferrite that was later assembled into a U shape with other ferrite and potted in a mu-metal can along with the transformer bobbins. | ||
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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. | ||
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 4 kV charge line into a 4 Ω 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. | ||
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The 4 kV supply was charged into a 4 Ω 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 [[C-5|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. | ||
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We changed the laser trim to be parallel to the current path along the outside edges. | We changed the laser trim to be parallel to the current path along the outside edges. | ||
That’s what was used in manufacturing for calibrating the risetime of the P6303. | That’s what was used in manufacturing for calibrating the risetime of the P6303. | ||
Also interesting, the P6303 required 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 | ||