Re: [time-nuts] Replacement fan in SR620
Volker, On 02/02/14 01:51, Volker Esper wrote: Magnus, I took an EBMPabst 624. Pabst has a good reputation. Papst is known good brand. I have seen another brand fail miserably so this is why I am asking. The original fan is a Delta Electronics DFB0624 H, Dimensions are 60mm x 60mm x 25mm, DC24V 0.11A Yes, and the EBM-Papst 624 matches it well. The Papst seems to have much lower noise from the datasheet. BTW. Both my SR620 checks out well. One of them was supposedly diagnosed with flicker. I still need to do the sensitivity part of the measurements, but lacking a suitable RF generator I can't do it smoothly. The fan in the new TIC locks itself into one position, so I had to help it. I don't know if it is worth the trouble to open it up, clean and lubricate. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
On 02/02/14 03:43, Charles Steinmetz wrote: Jarl wrote: In my SR620 the fan is a Delta DBF0624H. It is a 60x60x25 mm fan, 24V /0.11A. Mine, too. Does anyone know the airflow rating of the Delta fan? It does not appear to move as much air as it should (at least not if the idea is to hold the interior at a fixed temperature) -- every SR620 I've used has the fan running at full speed by the time it's been on for 10 minutes, unless the ambient temperature is less than 17-18C. On the one hand, it would be nice to move more air so the internal temperature is more tightly regulated; but on the other hand, it would also be nice if the fan were quieter. It is unlikely we can have both. The fact that the original fan seems marginal counsels against replacing it with one that moves less air. Well, considering the conditions it can't do much else. The thermal design of the 620 is far from optimal. The thermistor is located in a tunnel between the interior of the instrument and the exterior, with the fan blowing directly across it through the tunnel. So, the fan startup is an ugly process of fits and starts as the instrument warms up. Also, the air inlets seem to be too small and the internal airflow was not properly designed to circulate cooling air where it needs to go. If the heat sources where well coupled to the air-flow, which they are not, and the flow-path as low air-flow resistance, which it also doesn't have, requires the fan to work at high rate to get any air move, and to get the thermistor happy. I have toyed with the idea of cutting a slot maybe 4 long and 1/8 tall in the right wall of the chassis at the rear, above the four TO-220 devices mounted there -- and perhaps another slot about the same size in the top cover above those devices. Also, maybe attaching some internal baffles to the top cover to channel airflow where it is needed. You can mount a fan to create a steady flow on the right side, and that way cool off much of the heat there. I installed a terminal strip on the GPIB connector mounting screw and relocated the thermistor there in my SR620s (in the general vicinity of the oscillators). (However, note that stabilizing the internal oscillator temperature is not really very important for most of us, because time nuts generally use an external time base. In that case, it is probably more important that the temperature of the triggers and interpolators is held constant.) Well, we *do* care about a stable internal temperature, since it will also shift calibration factors, so the stabler the internal temperature is and hence various shifts which is being compensate, the more accurate it becomes. With the thermistors relocated as I have described, the fans start up as they should (monotonically, speeding up smoothly from stopped to full speed without any fits and starts). They still reach full speed in 10 minutes or so, so at the end of the day I don't think I've really changed anything except the aesthetics of the fan startup. (IMO, the change is worth it just for that, but there does not seem to be any operational improvement.) If you try to achieve the goal I think it will require a different approach. Perhaps SRS did not intend to regulate the interior temperature of the SR620 -- maybe they just wanted it to warm up faster (if you did away with the thermistor and had the fan run full speed whenever the counter was on, it would presumably take longer to warm up). Maybe, would make kind of sense, on the other hand, they could have achieve both quick heat-up and stable but lower temperature and quieter if they wanted. Anyway -- does anybody have an old Delta catalog or datasheet that specifies the airflow rating of the original Delta fan? It would indeed be interesting. The Papst 624 seems quite capable little critter and there seem to be some magic to the 624 number matching, which doesn't seem to be accidental. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Magnus wrote: If the heat sources where well coupled to the air-flow, which they are not, and the flow-path as low air-flow resistance, which it also doesn't have, requires the fan to work at high rate to get any air move, and to get the thermistor happy. My point was, the thermistor is never happy. It always wants more cooling. So it spins the fan up to full speed and is still too hot to reach equlibrium. You can mount a fan to create a steady flow on the right side, and that way cool off much of the heat there. You mean an internal fan, I take it. That still doesn't solve the problem of too little air moving through the box to lower the internal temperature to the target value in normal room ambient temperatures. Well, we *do* care about a stable internal temperature, since it will also shift calibration factors, so the stabler the internal temperature is and hence various shifts which is being compensate, the more accurate it becomes. Right. But unless the thermal design has been optimized (and it has not, on the SR620), you have to choose which part of the interior you want to be regulated to a constant temperature. The very worst possible choice is to put the thermistor in the exhaust stream of the fan (where SRS put it). It needs to be somewhere inside the box, and where you put it determines what part of the interior is regulated. Of course, all of this assumes that you use a fan that moves enough air to actually reach equilibrium before it gets to full speed. The stock fan doesn't, so NO place inside the box is regulated to a constant temperature, except in very cold ambient temperatures. Perhaps SRS did not intend to regulate the interior temperature of the SR620 -- maybe they just wanted it to warm up faster (if you did away with the thermistor and had the fan run full speed whenever the counter was on, it would presumably take longer to warm up). Maybe, would make kind of sense, on the other hand, they could have achieve both quick heat-up and stable but lower temperature and quieter if they wanted. Yes, they could have. So, the question is, do we just replace fans when they go bad and live with the poor thermal design, or do we try to improve the thermal design? If we want to improve the thermal design, the methods available to us are: (i) use a fan that moves more air, so the location of the thermistor is actually regulated to a constant temperature in normal ambient temperatures (not just in very cold ambient temperatures); (ii) relocate the thermistor to the most temperature-critical area inside the instrument; (iii) make additional air inlet holes, strategically placed to evenly cool the various zones of the interior; and (iv) add air baffles inside the box to evenly cool the various zones of the interior. It would indeed be interesting. The Papst 624 seems quite capable little critter and there seem to be some magic to the 624 number matching, which doesn't seem to be accidental. No magic. 624 just means that it is a 60x60mm fan that runs on 24v. Most fan manufacturers make a dozen or more fans with all different current draws, air movement, noise, number of fan blades, bearings, etc., etc., all with 624 in the part number (or whatever code that manufacturer uses for 60x60@24v -- 0624, 2406, etc.). Papst makes 624HH, 624N, 624/2H3P, 624H, 624M, 624/2HH, 624L, 624J, 624F, etc. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
On 02/02/14 18:47, Charles Steinmetz wrote: Magnus wrote: If the heat sources where well coupled to the air-flow, which they are not, and the flow-path as low air-flow resistance, which it also doesn't have, requires the fan to work at high rate to get any air move, and to get the thermistor happy. My point was, the thermistor is never happy. It always wants more cooling. So it spins the fan up to full speed and is still too hot to reach equlibrium. Which only means that the thermistor setup is shifted and needs to be adjusted to achieve the goal. You can mount a fan to create a steady flow on the right side, and that way cool off much of the heat there. You mean an internal fan, I take it. That still doesn't solve the problem of too little air moving through the box to lower the internal temperature to the target value in normal room ambient temperatures. No, I mean an external fan. The box have far to little air intake, as you have already pointed out, and I agree fully. Well, we *do* care about a stable internal temperature, since it will also shift calibration factors, so the stabler the internal temperature is and hence various shifts which is being compensate, the more accurate it becomes. Right. But unless the thermal design has been optimized (and it has not, on the SR620), you have to choose which part of the interior you want to be regulated to a constant temperature. The very worst possible choice is to put the thermistor in the exhaust stream of the fan (where SRS put it). It needs to be somewhere inside the box, and where you put it determines what part of the interior is regulated. Of course, all of this assumes that you use a fan that moves enough air to actually reach equilibrium before it gets to full speed. The stock fan doesn't, so NO place inside the box is regulated to a constant temperature, except in very cold ambient temperatures. I agree. There is many things which needs to be fixed to get there, there is no single silver-bullet to solve it all. Perhaps SRS did not intend to regulate the interior temperature of the SR620 -- maybe they just wanted it to warm up faster (if you did away with the thermistor and had the fan run full speed whenever the counter was on, it would presumably take longer to warm up). Maybe, would make kind of sense, on the other hand, they could have achieve both quick heat-up and stable but lower temperature and quieter if they wanted. Yes, they could have. So, the question is, do we just replace fans when they go bad and live with the poor thermal design, or do we try to improve the thermal design? If we want to improve the thermal design, the methods available to us are: (i) use a fan that moves more air, so the location of the thermistor is actually regulated to a constant temperature in normal ambient temperatures (not just in very cold ambient temperatures); (ii) relocate the thermistor to the most temperature-critical area inside the instrument; (iii) make additional air inlet holes, strategically placed to evenly cool the various zones of the interior; and (iv) add air baffles inside the box to evenly cool the various zones of the interior. I think a sub-set of these are needed, but you also need to include (v) change the balance-point for the thermistor stabilization. I think the single biggest problem is too little air inlet, which forces the fan to run in stupidly high speed without actually do much, as the air input has too low cross-section and with several small holes you need to create a large pressure difference in order to achieve the air flow wanted. Also, those holes help to create noise as they are not shaped to avoid turbulence. Best way is just achieve large enough cross-section. It would indeed be interesting. The Papst 624 seems quite capable little critter and there seem to be some magic to the 624 number matching, which doesn't seem to be accidental. No magic. 624 just means that it is a 60x60mm fan that runs on 24v. Most fan manufacturers make a dozen or more fans with all different current draws, air movement, noise, number of fan blades, bearings, etc., etc., all with 624 in the part number (or whatever code that manufacturer uses for 60x60@24v -- 0624, 2406, etc.). Papst makes 624HH, 624N, 624/2H3P, 624H, 624M, 624/2HH, 624L, 624J, 624F, etc. Ah, makes sense. It was a long time I looked at fan details myself. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Magnus wrote: My point was, the thermistor is never happy. It always wants more cooling. So it spins the fan up to full speed and is still too hot to reach equlibrium. Which only means that the thermistor setup is shifted and needs to be adjusted to achieve the goal. * * * So, the question is, do we just replace fans when they go bad and live with the poor thermal design, or do we try to improve the thermal design? If we want to improve the thermal design, the methods available to us are: I think a sub-set of these are needed, but you also need to include (v) change the balance-point for the thermistor stabilization. Well, sure, you can raise the setpoint until the fan slows down and regulates the temperature, but then the regulated temperature would be too high. In other words, if the fan cannot keep things cool enough by running at full speed, raising the set-point so the fan runs slower is not the right answer even if it does result in some approximation to isothermy. [Note that adjusting the setpoint *down* will have no effect -- the fan already cannot cool the instrument enough to reach equilibrium.] I think the single biggest problem is too little air inlet, which forces the fan to run in stupidly high speed without actually do much, as the air input has too low cross-section and with several small holes you need to create a large pressure difference in order to achieve the air flow wanted. Also, those holes help to create noise as they are not shaped to avoid turbulence. Best way is just achieve large enough cross-section. I have experimented with cardboard top covers that have various holes in them. My conclusion is that even with more air inlet area, you still want more cfm of air flow (i.e., a stronger fan). You also need to adjust the airflow to the various sections of the interior to keep everything sufficiently cool. As it is, there would be way too much temperature variation from one part of the interior to another even if you did reach a regulated equilibrium for the thermistor location (wherever you put the thermistor). Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
A little off topic but It seems many instruments (the SR620 and 53132A included) would work best with an internal fan. (A closed system, not exchanging outside air). Possibly with some sort of internal/external heat sink if needed. Or in high power situations outside air would flow through a hollow heatsink (again not exchanging outside and internal air). If nothing else this would keep dust out. Since fan filters can really restrict air-flow and without a filter dust on circuit boards can act as on thermal insulator leading to overheating while conducting static. Thomas Knox Date: Sun, 2 Feb 2014 19:17:03 +0100 From: mag...@rubidium.dyndns.org To: time-nuts@febo.com Subject: Re: [time-nuts] Replacement fan in SR620 On 02/02/14 18:47, Charles Steinmetz wrote: Magnus wrote: If the heat sources where well coupled to the air-flow, which they are not, and the flow-path as low air-flow resistance, which it also doesn't have, requires the fan to work at high rate to get any air move, and to get the thermistor happy. My point was, the thermistor is never happy. It always wants more cooling. So it spins the fan up to full speed and is still too hot to reach equlibrium. Which only means that the thermistor setup is shifted and needs to be adjusted to achieve the goal. You can mount a fan to create a steady flow on the right side, and that way cool off much of the heat there. You mean an internal fan, I take it. That still doesn't solve the problem of too little air moving through the box to lower the internal temperature to the target value in normal room ambient temperatures. No, I mean an external fan. The box have far to little air intake, as you have already pointed out, and I agree fully. Well, we *do* care about a stable internal temperature, since it will also shift calibration factors, so the stabler the internal temperature is and hence various shifts which is being compensate, the more accurate it becomes. Right. But unless the thermal design has been optimized (and it has not, on the SR620), you have to choose which part of the interior you want to be regulated to a constant temperature. The very worst possible choice is to put the thermistor in the exhaust stream of the fan (where SRS put it). It needs to be somewhere inside the box, and where you put it determines what part of the interior is regulated. Of course, all of this assumes that you use a fan that moves enough air to actually reach equilibrium before it gets to full speed. The stock fan doesn't, so NO place inside the box is regulated to a constant temperature, except in very cold ambient temperatures. I agree. There is many things which needs to be fixed to get there, there is no single silver-bullet to solve it all. Perhaps SRS did not intend to regulate the interior temperature of the SR620 -- maybe they just wanted it to warm up faster (if you did away with the thermistor and had the fan run full speed whenever the counter was on, it would presumably take longer to warm up). Maybe, would make kind of sense, on the other hand, they could have achieve both quick heat-up and stable but lower temperature and quieter if they wanted. Yes, they could have. So, the question is, do we just replace fans when they go bad and live with the poor thermal design, or do we try to improve the thermal design? If we want to improve the thermal design, the methods available to us are: (i) use a fan that moves more air, so the location of the thermistor is actually regulated to a constant temperature in normal ambient temperatures (not just in very cold ambient temperatures); (ii) relocate the thermistor to the most temperature-critical area inside the instrument; (iii) make additional air inlet holes, strategically placed to evenly cool the various zones of the interior; and (iv) add air baffles inside the box to evenly cool the various zones of the interior. I think a sub-set of these are needed, but you also need to include (v) change the balance-point for the thermistor stabilization. I think the single biggest problem is too little air inlet, which forces the fan to run in stupidly high speed without actually do much, as the air input has too low cross-section and with several small holes you need to create a large pressure difference in order to achieve the air flow wanted. Also, those holes help to create noise as they are not shaped to avoid turbulence. Best way is just achieve large enough cross-section. It would indeed be interesting. The Papst 624 seems quite capable little critter and there seem to be some magic to the 624 number matching, which doesn't seem to be accidental. No magic. 624 just means that it is a 60x60mm fan that runs on 24v. Most fan manufacturers make a dozen or more fans with all different current draws, air movement, noise, number of fan
Re: [time-nuts] Replacement fan in SR620
Magnus, Yes, and the EBM-Papst 624 matches it well. The Papst seems to have much lower noise from the datasheet. There's yet another problem: the mechanical construction conducts the fan noise to the case, so the noise is kind of amplified by the case. I felt somewhat disappointed after replacing the fan, don't expect too much. I just read the postings of Charles and I, too, was unhappy with the startup behaviour. I changed the values of the driver circuit, but kept the sensor in the tunnel. That helped making the motor speed rising monotonically. The air inlets are too small - that's true, if you need so much air flow. We agree that the fan speed is at it's maximum, not at it's equilibrium. So I tried to separate the heat sources. At the right (and left) side of the case various voltage regulators heat the side wall. I placed a heat sink with vertikal fins from the outside on that wall, the screws of the regulators screwed into the aluminium. I'll further place a wall inside the counter right before those heating parts. The experiment isn't completed yet, but I'm keen enough to claim that it'll help to stabilize internal temperature particularly at the sensitive components. Volker ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
On 02/02/14 20:16, Charles Steinmetz wrote: Magnus wrote: My point was, the thermistor is never happy. It always wants more cooling. So it spins the fan up to full speed and is still too hot to reach equlibrium. Which only means that the thermistor setup is shifted and needs to be adjusted to achieve the goal. * * * So, the question is, do we just replace fans when they go bad and live with the poor thermal design, or do we try to improve the thermal design? If we want to improve the thermal design, the methods available to us are: I think a sub-set of these are needed, but you also need to include (v) change the balance-point for the thermistor stabilization. Well, sure, you can raise the setpoint until the fan slows down and regulates the temperature, but then the regulated temperature would be too high. In other words, if the fan cannot keep things cool enough by running at full speed, raising the set-point so the fan runs slower is not the right answer even if it does result in some approximation to isothermy. [Note that adjusting the setpoint *down* will have no effect -- the fan already cannot cool the instrument enough to reach equilibrium.] I'm not discussing it as a single measure, but rather a thing you can look at only after you got air-flow working much better. I think the single biggest problem is too little air inlet, which forces the fan to run in stupidly high speed without actually do much, as the air input has too low cross-section and with several small holes you need to create a large pressure difference in order to achieve the air flow wanted. Also, those holes help to create noise as they are not shaped to avoid turbulence. Best way is just achieve large enough cross-section. I have experimented with cardboard top covers that have various holes in them. My conclusion is that even with more air inlet area, you still want more cfm of air flow (i.e., a stronger fan). You also need to adjust the airflow to the various sections of the interior to keep everything sufficiently cool. As it is, there would be way too much temperature variation from one part of the interior to another even if you did reach a regulated equilibrium for the thermistor location (wherever you put the thermistor). I agree. You need both, but just tossing in a stronger fan isn't going to cut it either. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
On 02/02/14 20:28, Tom Knox wrote: A little off topic but It seems many instruments (the SR620 and 53132A included) would work best with an internal fan. (A closed system, not exchanging outside air). Possibly with some sort of internal/external heat sink if needed. Or in high power situations outside air would flow through a hollow heatsink (again not exchanging outside and internal air). If nothing else this would keep dust out. Since fan filters can really restrict air-flow and without a filter dust on circuit boards can act as on thermal insulator leading to overheating while conducting static. Good point. A fan in a closed environment will survive longer, or rather, won't degrade as fast as it possibly would do. These days I would assume that heat-pipes would be used to move heat to a large external heat-sink. It's fairly cheap these days. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
On 02/02/14 20:13, Volker Esper wrote: Magnus, Yes, and the EBM-Papst 624 matches it well. The Papst seems to have much lower noise from the datasheet. There's yet another problem: the mechanical construction conducts the fan noise to the case, so the noise is kind of amplified by the case. I felt somewhat disappointed after replacing the fan, don't expect too much. You mean the fact that the lid acts like a speaker membrane? So true. The best cases I have seen have suspended mounting for fans and other vibration-makers (hard-disks). I just read the postings of Charles and I, too, was unhappy with the startup behaviour. I changed the values of the driver circuit, but kept the sensor in the tunnel. That helped making the motor speed rising monotonically. The air inlets are too small - that's true, if you need so much air flow. We agree that the fan speed is at it's maximum, not at it's equilibrium. So I tried to separate the heat sources. At the right (and left) side of the case various voltage regulators heat the side wall. I placed a heat sink with vertikal fins from the outside on that wall, the screws of the regulators screwed into the aluminium. I'll further place a wall inside the counter right before those heating parts. The experiment isn't completed yet, but I'm keen enough to claim that it'll help to stabilize internal temperature particularly at the sensitive components. It's indeed clear that the voltage regulators contribute a lot of heat. That's why I proposed to put a fan on the outside. As built, it is easy to cook it when it is put too crowded. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Magnus wrote: I agree. You need both, but just tossing in a stronger fan isn't going to cut it either. Very true. You need to attack all of the problems to fix it. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Magnus wrote: These days I would assume that heat-pipes would be used to move heat to a large external heat-sink. It's fairly cheap these days. I have looked into heat pipes for several projects, and in the end have never used them. The main problem is that almost every solution is customized. No trouble if you make PC motherboards or consumer-grade stereo amplifiers 50,000 at a time. But most instruments are made in quantities of 5,000 or fewer, and it takes many years to make (sell) even that number. With production numbers that low, the bean counters want the design and tooling costs amortized over the first year's production -- maybe only 100-500 units -- which can raise the retail price by a factor of 2-10. At least that's what I've found. Also, most heat-pipe systems are gravity-fed, so if someone turns your product on its side they can burn it down. (I almost always operate my portable spectrum analyzer (HP8591E) standing on its rear feet with the screen pointing up. I can foresee someone with limited bench space setting an SR620 on its side.) Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Charles, On 02/02/14 21:06, Charles Steinmetz wrote: Magnus wrote: I agree. You need both, but just tossing in a stronger fan isn't going to cut it either. Very true. You need to attack all of the problems to fix it. Well, maybe not all of them, but there is several key areas that together form the basic problem. We also have ECL dispersed throughout the right side of the board which also needs cooling. Most of that can be handled through general cooling if only air flows there. I just checked the lab, and the SR620 standing on the somewhat crowded bench and with a SR620 manual laying on top of it was cooler than the SR620 sitting up among the other instruments. As I re-checked the slots for air inlet I was amazed how little there where. Letting more air in on the back would work if there is large enough air at the back, then setting a central baffle so that it at least sweeps over the electronics up to the front before being sucked over the CPU into the fan. Also, the fan-noise did not change a lot by drying to damp the top lid, so it seems the fan emits it mostly as a direct mode. The older unit has a high hiss to its fan while the newer has a more rattling sound to it. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Magnus wrote: Also, the fan-noise did not change a lot by drying to damp the top lid, so it seems the fan emits it mostly as a direct mode. The older unit has a high hiss to its fan That is what I have observed, as well. The noise is mostly fan blade noise and some bearing noise coming directly out the back of the unit. I did not find that the inlet vents were a significant source of noise, or that increasing the inlet area caused the fan itself to run quieter. You probably wouldn't notice a substantial noise reduction until you got down to a fan with a 15-18 dBA noise rating, and that would move so little air that you'd probably fry the counter. The Papst fan has about the same noise rating as the original Delta, so I wouldn't expect changing the fan to have a big effect on the amount of noise (but, as you say, the noise spectrum may be different). Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
On 02/02/14 21:34, Charles Steinmetz wrote: Magnus wrote: These days I would assume that heat-pipes would be used to move heat to a large external heat-sink. It's fairly cheap these days. I have looked into heat pipes for several projects, and in the end have never used them. The main problem is that almost every solution is customized. No trouble if you make PC motherboards or consumer-grade stereo amplifiers 50,000 at a time. But most instruments are made in quantities of 5,000 or fewer, and it takes many years to make (sell) even that number. With production numbers that low, the bean counters want the design and tooling costs amortized over the first year's production -- maybe only 100-500 units -- which can raise the retail price by a factor of 2-10. At least that's what I've found. Also, most heat-pipe systems are gravity-fed, so if someone turns your product on its side they can burn it down. (I almost always operate my portable spectrum analyzer (HP8591E) standing on its rear feet with the screen pointing up. I can foresee someone with limited bench space setting an SR620 on its side.) Good point. The SR620 doesn't stand on the back very well, maybe on it's side, but that helps to close the little air intake there is... Decided to finally toss the original box for my SIA-3000. It's just big and messy. Not tossing the SIA-3000 itself, it's a keeper. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Charles, On 02/02/14 21:58, Charles Steinmetz wrote: Magnus wrote: Also, the fan-noise did not change a lot by drying to damp the top lid, so it seems the fan emits it mostly as a direct mode. The older unit has a high hiss to its fan That is what I have observed, as well. The noise is mostly fan blade noise and some bearing noise coming directly out the back of the unit. I did not find that the inlet vents were a significant source of noise, or that increasing the inlet area caused the fan itself to run quieter. You probably wouldn't notice a substantial noise reduction until you got down to a fan with a 15-18 dBA noise rating, and that would move so little air that you'd probably fry the counter. The Papst fan has about the same noise rating as the original Delta, so I wouldn't expect changing the fan to have a big effect on the amount of noise (but, as you say, the noise spectrum may be different). Well, with a ball-bearing noise it's much worse than fan-blade hiss. Fan-blade hiss is result of running at stupid speeds without achieving much. Anyway, I will probably get a new fan so I might as well get two. Finding out why the UPS won't start and parts of my rig with it is however higher up on the to-do list now that I figured that much out... and more clean-up. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
With an internal fan I think the covers actually can make a great heat exchanger as well. Often an instrument that is overheating will have portions of the case still cool. Perhaps the worst example of fan cooling is the Symetricom 512XA Phase Noise Test set. It is kind of out of place on such an otherwise exceptional produce. No offense meant to the Symmetricom engineers. It is one of the few product I have purchased new. Thomas Knox Date: Sun, 2 Feb 2014 20:42:54 +0100 From: mag...@rubidium.dyndns.org To: time-nuts@febo.com Subject: Re: [time-nuts] Replacement fan in SR620 On 02/02/14 20:28, Tom Knox wrote: A little off topic but It seems many instruments (the SR620 and 53132A included) would work best with an internal fan. (A closed system, not exchanging outside air). Possibly with some sort of internal/external heat sink if needed. Or in high power situations outside air would flow through a hollow heatsink (again not exchanging outside and internal air). If nothing else this would keep dust out. Since fan filters can really restrict air-flow and without a filter dust on circuit boards can act as on thermal insulator leading to overheating while conducting static. Good point. A fan in a closed environment will survive longer, or rather, won't degrade as fast as it possibly would do. These days I would assume that heat-pipes would be used to move heat to a large external heat-sink. It's fairly cheap these days. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Hi: There are some radios where the internal power supply heat degrades performance. The fix is to remove the power supply to an external box. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Replacement fan in SR620
Fellow time-nuts, I heard the fan in one of my SR620s and it didn't really was a nice sound. Has someone found a good replacement fan? Quieter would be nice. Considering performance checks and calibration this evening. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Magnus I have a big collector of fans, mostly for Agilent equipment not that it matters, let me know the dimensions I will see what I have that is quiet. Cheers; Thomas Knox Date: Sat, 1 Feb 2014 18:56:48 +0100 From: mag...@rubidium.dyndns.org To: time-nuts@febo.com Subject: [time-nuts] Replacement fan in SR620 Fellow time-nuts, I heard the fan in one of my SR620s and it didn't really was a nice sound. Has someone found a good replacement fan? Quieter would be nice. Considering performance checks and calibration this evening. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Magnus, I took an EBMPabst 624. Pabst has a good reputation. The original fan is a Delta Electronics DFB0624 H, Dimensions are 60mm x 60mm x 25mm, DC24V 0.11A Volker Am 01.02.2014 18:56, schrieb Magnus Danielson: Fellow time-nuts, I heard the fan in one of my SR620s and it didn't really was a nice sound. Has someone found a good replacement fan? Quieter would be nice. Considering performance checks and calibration this evening. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Replacement fan in SR620
Jarl wrote: In my SR620 the fan is a Delta DBF0624H. It is a 60x60x25 mm fan, 24V /0.11A. Mine, too. Does anyone know the airflow rating of the Delta fan? It does not appear to move as much air as it should (at least not if the idea is to hold the interior at a fixed temperature) -- every SR620 I've used has the fan running at full speed by the time it's been on for 10 minutes, unless the ambient temperature is less than 17-18C. On the one hand, it would be nice to move more air so the internal temperature is more tightly regulated; but on the other hand, it would also be nice if the fan were quieter. It is unlikely we can have both. The fact that the original fan seems marginal counsels against replacing it with one that moves less air. The thermal design of the 620 is far from optimal. The thermistor is located in a tunnel between the interior of the instrument and the exterior, with the fan blowing directly across it through the tunnel. So, the fan startup is an ugly process of fits and starts as the instrument warms up. Also, the air inlets seem to be too small and the internal airflow was not properly designed to circulate cooling air where it needs to go. I have toyed with the idea of cutting a slot maybe 4 long and 1/8 tall in the right wall of the chassis at the rear, above the four TO-220 devices mounted there -- and perhaps another slot about the same size in the top cover above those devices. Also, maybe attaching some internal baffles to the top cover to channel airflow where it is needed. I installed a terminal strip on the GPIB connector mounting screw and relocated the thermistor there in my SR620s (in the general vicinity of the oscillators). (However, note that stabilizing the internal oscillator temperature is not really very important for most of us, because time nuts generally use an external time base. In that case, it is probably more important that the temperature of the triggers and interpolators is held constant.) With the thermistors relocated as I have described, the fans start up as they should (monotonically, speeding up smoothly from stopped to full speed without any fits and starts). They still reach full speed in 10 minutes or so, so at the end of the day I don't think I've really changed anything except the aesthetics of the fan startup. (IMO, the change is worth it just for that, but there does not seem to be any operational improvement.) Perhaps SRS did not intend to regulate the interior temperature of the SR620 -- maybe they just wanted it to warm up faster (if you did away with the thermistor and had the fan run full speed whenever the counter was on, it would presumably take longer to warm up). Anyway -- does anybody have an old Delta catalog or datasheet that specifies the airflow rating of the original Delta fan? Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
