Although the Programmable Power Resistor re-uses some components, many design ideas and a good portion of the software of the Programmable Decade Resistor (Programmable Precision Resistor), there were many changes and also some improvements regarding some aspects of the mechanical construction and the code.
The Programmable Power Resistor consists of two large boards: The User Interface and Controller Board and the Relay and Interface Board. Because of the use of relays that isolate the input from the circuits, all circuits can be and therefore are earth-referenced.
The HP/Agilent 6632B is a remarkable power supply. There are some similarities with the mobile communication DC source 66309D I “repaired” recently: The 6632B is optimized for a fast transient response and it has a low current range too. But the circuit and its properties differ significantly. One important aspect: Where the 66309D only has a downprogrammer that doesn’t track the current setpoint, the 6632B goes all-in: It’s a two-quadrant power supply - able to source and sink current over the full operating range from 0-20V at 0-5A in CV and CC mode.
In the last post we had a look at a simple topology that allows us to switch between a series and a parallel connection of two resistors: Now we’ll nest these structures so that we have four resistors:
For the performance checks and calibration of my Agilent 6811B AC Power Source/Analyzer (375VA) I need a 20 Ohm resistor with a ton of power handling capability. The original plan was to mount 8 wire wound 50W resistors on a heat sink and be done with it. Then I thought: Why not reuse all the code I’ve already written for the programmable resistor and build a programmable high power resistor that can complement my DC load for AC applications.
A few days ago I got my hands on a faulty Agilent 66309D Mobile Communication DC Source. To be honest, I don’t think I need it, but it was pretty cheap and I was looking for something to either repair or potentially salvage the case of.
Currently, the unit’s setpoint accuracy isn’t all that great (readback resolution is limited as well, but shows the offset): Regardless of the range it has an offset of about +20 mA. Sure, for a unit capable of 60 A that seems reasonable, and well within its specs of ±0.1% ±75 mA. But since I’ll use it in the low range (6A) most of the time and likely often even well below 1A that doesn’t seem too great, does it?
I recently got my hands on a HP 6060B System DC Electronic Load (later also sold as Agilent 6060B). My unit has option 020 installed: Comically large binding posts also on the front panel. This option certainly is not unheard of, but not too common either. Retrofitting is possible, but can be quite some work.
I got my Agilent 6611B AC power source/analyzer a few weeks back, but hadn’t used it as much as I wanted. The reason was simple: The connections are made with rear mounted screw terminals - hence it was just a bit inconvenient to interface with products and circuits. The solution was really simple: A Hammond Manufactoring enclosure equipped with a European " Schuko"-style power outlet and some additional safety-banana jacks for prototyping.
For projects like the programmable resistor I was looking for a case, preferably made of aluminum and 19" compatible. In order to save some space on the desk I hoped to find one with a width of 42HP (i. e. half width). What I found was a beautiful case made by ELMA (2 RU, 42HP), called Stylebox 15 Standard.
For a long time I wanted to build an SCPI capable thermometer to keep track of the ambient temperature in my small lab. The list of requirements was fairly short: Reasonably high precision (Sensor with <= 0.3°C max. uncertainty) Power and SCPI communication over USB Compact enclosure with a display Design After researching temperature sensors I chose a Texas Instruments TMP117M temperature sensor with quite impressive specs. With an accuracy of ±0.1°C (max.) between 25°C to 50°C and ±0.05°C (typ.) between 0°C and 70°C it is much more than good enough for my purpose, but why not overspec the sensor a bit? Because of the tiny package (WSON6, 2mm x 2mm) I was a bit nervous. As it later turned out, soldering the IC using a hot air soldering station was a bit more time consuming than e. g. a typical SOIC package (preparation), but not that difficult.
Many older HP/Agilent instrument share a similar feet design. There are at least two different types though: One with a metal part to prop up the instrument and one without it that can be used on all four corners. The feet can be detached from the instrument, e. g. for use in 19" racks. This also means they got thrown away too often, so that many used instruments come without them. For some time they were available on ebay at a reasonable price.