标签: spectrometer

In a university chemistry department, there is a broad range of equipment, ranging from technologically recent equipment to old equipment, older equipment, and finally the "designers-have-been-grave-stoned for twenty years" equipment. One day a call came in from the Mass-Spec Lab: A quadrupole mass spectrometer, made in the UK, was alarming in standby mode but not in operate mode. Fortunately, we had a set of schematics for the instrument, but the folks across the pond draw things a little differently. Fortunately, deciphering the drawings didn't take long using my super secret decoder ring (a.k.a., paper, pencil, and pencil sharpener). The alarm was coming from a relay board that distributed 24Vdc power to three off-board circuits. On this particular machine, power for each circuit goes through a dedicated set of two (one operate and one interlock) SPDT relays rated to 5A. Both relays are energized to pass power in the operate mode and de-energized in standby mode. Any other relay combinations sounds an alarm. The NC contacts on each relay go to alarm logic, where they are XORed to each other. When the "operate" relay is de-energized, 24V (applied to the COM) passes through a 100kΩ to the NO contact, providing 24V low current signal to the second relay's COM. This is needed at the second relay so when it is de-energized there is a "high" logic signal to the alarm logic through the NC contact. A visual inspection while switching "standby" to "operate" showed that all of the relays were toggling. Using a low-power binocular microscope, the relay contacts where inspected. As expected, the NO contacts showed pitting for current switching. The NC contacts appeared clean and pristine, also as expected since they switched very low current. Measurements with an ohmmeter showed some relays having NC contact resistance ranging from half an ohm to tens of ohms on repetitive relay cycling using a bench power supply. One relay randomly measured higher resistance to megaohms. But continued cycling slowly reduced the resistance. After ordering an identical relay and replacing it, the alarm issue went away. But a few months later the problem was back. This time another relay had the resistance issue. We ordered several identical relays. But the real quandary began after we installed one of the new relays. The alarm issue persisted and was traced back to the new relay. Several of these new relays were tested and a few showed the same contact issue. A "good" relay was selected and installed, getting the instrument back in operation. But what was going on?   After some hypothesis, analysis, meditation, perusing of datasheets on different kinds of relays, a headache, shot o'wiskey, dinner, more shots o'whiskey, sleep, hangover, breakfast, I began to formulate a theory. The relay uses silver contact material, which is correct for switching moderate power currents. But the COM-NC circuit is a microamp (small-signal) circuit. Small-signal relay contacts always use gold plating. Why? Because gold doesn't oxidise. Silver is more durable and withstands arcing better than gold, but silver oxidizes. The arcing cuts through this oxidation. Microamp current at 24V does not arc and, therefore, does not clear the oxidation. Over time the oxidation builds up, causing contact resistance problems. Obviously a design goof or oversight by engineers on the big island. (This might be one of the reasons why in 1620 a small group of them left and started a colony called Plymouth.)     So what to do? One solution was to add a load resistor to the NC side to pull more current, thereby causing arcing to clear the oxidation. But this would not work on the second relay due to the 100k resistor. What we needed was a relay with silver on the COM-NO side and gold on the COM-NC side and also fit in place of the original relay. Right! What else? Re-designing the circuit was not an option due to down-time and budget constraints. Hum! What followed almost defies commonsense, but we are academia and the rules do not apply. Take a relay, remove the cover then disassemble (see picture). Go to the junk drawer and get an edge-card connector with gold contacts and remove a contact. Un-curl it. Use a rounded-end punch and piece of hardwood to make two bowl-like dimples. Cut out the dimpled areas forming small pieces for soldering over the NC contacts. File the NC contacts down to make room for the gold contacts. Tin the NC contacts. Using the old-school silicon heat-sink compound and wooden tooth-pick, carefully put heat-sink on the convex side of the dimpled contact. This will keep solder from flowing onto that surface (Ssshhh! This is a secret technique so don't tell anyone.) The heat-sink will also hold the small contact to the toothpick so it can be flipped over. Tin the concave side. Heat the relay contact to melt the tinning, then carefully place the concave side of the gold contact over the relay contact and wait for it to heat. Remove the heat and carefully hold until the solder cools. Repeat process for other relay contact. Clean off heat sink. Reassemble relay but leave the cover off. Use bench power supply to cycle the relay and verify the NC contact arm flexes slightly, bending the NC arm as needed. This insures there is contact pressure. Put on cover and store this "special" relay. Breath deeply, have a cup of coffee, and stretch. Move onto the next project—plastic membrane switch/label eaten off the hot plate... chemists!   About two years later, the instrument failed again, alarming in stand-by. Testing showed one "bad" relay and another following suit. Repeat above process on another relay. We installed these "special" relays and tested. No alarms! Yesss! It has been three months now, and only time will tell if these relays fail. The modification for one takes about an hour of delicate work. A second identical mass-spec has since arrived in the department, improving odds on opportunities for us to mod more relays. But, hey, America's got talent! Richard Bedell, electrical engineer, submitted this article as part of Frankenstein's Fix, a design contest hosted by EE Times (US).  

  Next we point the spectrometer at another area (again, let's say a pinkish area to keep with our previous example) and we tweak our light sources until the new RGB values being reflected from the pinkish area are the same as the old RGB values from the brownish area. Initially we are amazed to see that all of the colors on the panel appear to be unchanged. Now we take a piece of white card that covers the entire panel apart from a cut-out that reveals only the original pinkish area ... which magically changes into the brownish color. But when we remove the white card to reveal the entire panel, the pinkish area returns to its original pinkish hue. How can this be? In fact, what's happening is that your brain maintains a three-dimensional color-map in which every color is weighted in relation to every other color. Thus, when you can see the whole panel, your brain automatically calculates all of the color relationships and adjusts what you're actually seeing to match what it thinks you should be seeing. By comparison, if you can see only one shape, then your brain has no other recourse than to assume that this shape's color is determined by the red, blue, and green components that are being reflected from the shape. It's only if you can see a shape's color in the context of all of the other shapes' colors, then your brain does some incredibly nifty signal processing, determines what colors the various shapes should be, and corrects all of the colors before handing the information over to the conscious portion of your mind. All I can say is that you really have to see this to believe it – speaking of which... Performing this experiment for ourselves I would love to recreate this experiment and post it on YouTube so that everyone can see it for themselves. As we see from the discussions above, there are main three elements to this experiment: the three RGB light sources, the panel with the multicolored geometric shapes, and the spectrometer (or whatever we decide to use). The Lights: I don't think that laying my hands on three stage lights (with individual dimmers) along with three pure color RGB filters will pose a major problem. The Multicolored Panel: The panel with the multicolored geometric shapes is another issue. If we make it out of board – say 1.83 x 1.83 m – then it's going to be a pain to move around (suppose, for example, that I wanted to replicate this experiment as ESC or DAC next year). Also, if we have say 100 colored geometric areas (squares, rectangles, L-shapes, T-shapes) ... then this is going to cost a fortune in paint, because we would be using only a dribble from each can. But earlier today I had an idea... In the building in which you find my little office, I share the bay with a company called Out of the Box Exhibits . This is rather cool – they make incredibly low-cost trade show exhibits using cardboard structures clad with a tough canvas material upon which can be painted any design their customers desire. Even better, their graphics expert – Bruce Till – sits in the office next to mine. With Bruce's help, I could easily get a vibrant, multicolored canvas panel designed and printed, so all that remains is... The Spectrometer (or Equivalent): I remember looking into these a couple of years ago and they were not cheap. But technology has progressed in leaps and bounds, so there are several solutions that spring to mind. One possibility would be to somehow connect a digital camera to a PC running some sort of software application such that you could display what the camera was seeing (like our multicolored panel) in real-time on the PC screen. Another aspect to the software application would be that it would display a set of cross-hairs on the screen and that you could move these cross-hairs using your mouse or the arrow keys. Wherever the cross-hairs are on the screen, you would see a readout of the corresponding RGB values "under" the cross-hairs. An even simpler option (in some respects) would be to have a special application running on my iPad, which already has an inbuilt camera. But I know nothing about building iPad apps and I have no clue where to turn... So now it's over to you. Do you have a better alternative to my camera-PC combo or my creating an iPad app concept? Maybe you know someone who can create iPad apps. If you do have any ideas, please feel free to post a comment .... our operators (well, me, actually) are standing by...  

  Next we point the spectrometer at another area (again, let's say a pinkish area to keep with our previous example) and we tweak our light sources until the new RGB values being reflected from the pinkish area are the same as the old RGB values from the brownish area. Initially we are amazed to see that all of the colors on the panel appear to be unchanged. Now we take a piece of white card that covers the entire panel apart from a cut-out that reveals only the original pinkish area ... which magically changes into the brownish color. But when we remove the white card to reveal the entire panel, the pinkish area returns to its original pinkish hue. How can this be? In fact, what's happening is that your brain maintains a three-dimensional color-map in which every color is weighted in relation to every other color. Thus, when you can see the whole panel, your brain automatically calculates all of the color relationships and adjusts what you're actually seeing to match what it thinks you should be seeing. By comparison, if you can see only one shape, then your brain has no other recourse than to assume that this shape's color is determined by the red, blue, and green components that are being reflected from the shape. It's only if you can see a shape's color in the context of all of the other shapes' colors, then your brain does some incredibly nifty signal processing, determines what colors the various shapes should be, and corrects all of the colors before handing the information over to the conscious portion of your mind. All I can say is that you really have to see this to believe it – speaking of which... Performing this experiment for ourselves I would love to recreate this experiment and post it on YouTube so that everyone can see it for themselves. As we see from the discussions above, there are main three elements to this experiment: the three RGB light sources, the panel with the multicolored geometric shapes, and the spectrometer (or whatever we decide to use). The Lights: I don't think that laying my hands on three stage lights (with individual dimmers) along with three pure color RGB filters will pose a major problem. The Multicolored Panel: The panel with the multicolored geometric shapes is another issue. If we make it out of board – say 1.83 x 1.83 m – then it's going to be a pain to move around (suppose, for example, that I wanted to replicate this experiment as ESC or DAC next year). Also, if we have say 100 colored geometric areas (squares, rectangles, L-shapes, T-shapes) ... then this is going to cost a fortune in paint, because we would be using only a dribble from each can. But earlier today I had an idea... In the building in which you find my little office, I share the bay with a company called Out of the Box Exhibits . This is rather cool – they make incredibly low-cost trade show exhibits using cardboard structures clad with a tough canvas material upon which can be painted any design their customers desire. Even better, their graphics expert – Bruce Till – sits in the office next to mine. With Bruce's help, I could easily get a vibrant, multicolored canvas panel designed and printed, so all that remains is... The Spectrometer (or Equivalent): I remember looking into these a couple of years ago and they were not cheap. But technology has progressed in leaps and bounds, so there are several solutions that spring to mind. One possibility would be to somehow connect a digital camera to a PC running some sort of software application such that you could display what the camera was seeing (like our multicolored panel) in real-time on the PC screen. Another aspect to the software application would be that it would display a set of cross-hairs on the screen and that you could move these cross-hairs using your mouse or the arrow keys. Wherever the cross-hairs are on the screen, you would see a readout of the corresponding RGB values "under" the cross-hairs. An even simpler option (in some respects) would be to have a special application running on my iPad, which already has an inbuilt camera. But I know nothing about building iPad apps and I have no clue where to turn... So now it's over to you. Do you have a better alternative to my camera-PC combo or my creating an iPad app concept? Maybe you know someone who can create iPad apps. If you do have any ideas, please feel free to post a comment .... our operators (well, me, actually) are standing by...