Hot summer came to place where I live. It's good time to perform some experiments with Rigol scopes, which are as noisy as vacuum cleaner. I'd like to share with you results of my last research on power consumption, cooling, fans, etc. I have Rigol DS1052E and 1074Z-S - first consumes only 18-20W of power, whereas the second eats 25W of mains power. So the question is - is it possible to remove the fan? How much can I reduce the noise level? Let't try
Rigol DS1052EAt the beginning I wanted to find out which parts heat up the most. I don't have thermal imaging camera, so I used simple thermocouple meter. I attached thermocouples to several components with a thermocondictive sticky tape and measured hottest components:
So the hottest component is LM317 in power supply. Firstly I wanted to replace it with cheap Chinese switching converter but this may be not the best idea
I noticed that all ICs have no heat sinks. Then I ordered some heat sinks and have another try
IC with heat sink and thermocouple
And here comes the first fail during this experiment - measurement with no neat sinks I made day before, which was colder. The next day was much hotter (ambient temp in my room was 30'C!) and temperatures measured were higher than with no heat sinks! So, I don't know how much heat sinks improve cooling.
Anyway, the LM317 with no fan heats up to 90'C. Datasheet says the maximum temperature is 150'C. Any other components don't heat over 70'C. So this means, that
Rigol DS1052E doesn't need fan at all! To prove it, I powered up the scope, set highest sampling rate on two channels, turned on FFT, alternate trigger, measurements, ref channel, auto cursors, etc to make the scope as busy as possible, and then I left the scope for 8 hours. What happened after? Nothing. Scope was still working.
Although this test succeeded, I was worrying that having sauna inside the scope may reduce its lifetime. Then I check the impact of fan voltage on temperature of LM317 and FPGA in the scope. I measured noise level with my phone. No idea how accurate this measurement is, but it shows noise level approximately.
Here are the results of temperature measurement. I started with no fan and after half an hour I started to increase fan voltage by 2V on every 20 minutes.
Another chart shows temperature of LM317 and FPGA when themperature stabilized and fan noise level:
You see, that fan powered with 4V is practically noiseless but makes significant difference on temperature. Many people replaced Rigol's original fan with quieter one, but I had better idea. Let's just add a serial resistor to reduce fan voltage. So I added 100R resistor on fan cable as shown in the photo:
Final conclusion is that Rigol DS1052E doesn't need a fan, but it's better to add a 100R 1W resistor to lower it's voltage. This way
I reduced noise level from 32dB to 5dB!Remember to perform calibration after this mod, because ADC offset depends on the temperature. Power up the scope and left if for at least half an hour to stabilize temperature and then run self calibration.
To verify if scope is calibrated correctly you can run simple test - switch mode of operation from Y-T to roll mode, set vertical scale to 2mV/div and horizontal to 50s/div. Then power your scope as you should see something like this. When scope is cold there are some offsets on both channels but after it heats up, the offsets should reduce and remain stable then.
Rigol DS1074Z-SNext scope to mod is Rigol DS1074Z-S. I figured out that hottest components are Spartan 6 FPGA whis already has a huge heat sink and Freescale CPU. Power supply doesn't heat over 50'C even with no fan. This time I advice not to run the scope with no fan for long time. Freescale CPU heats up over 90'C so I glued a heat sink to it and to other large ICs.
I performed the same test with fan voltage, temperature and noise. You see that FPGA and CPU heats a lot and they could reach 100'C if I perform the test longer. That's why the fan is a must.
When assembling the scope I accidentally hit the power source shield with a screwdriver and it sounds like a bell. Noticed there's a fan next to the shield. Hmmmm? Maybe I should remove the shield? Lets try.
Red dots show noise level with power supply shield attached, green dots with no shield. Interesting phenomenon happens when voltage is between 6 and 8 volts - an air flow causes a resonance on the shield?
Again, as in DS1052, when voltage is low the fan is noiseless. So I added 100R 1W resistor on fan wire to have about 5V on the fan. Then I performed calibration and here's the result:
Conclusion - DS1074Z-S heats more than DS1052E and can't run without a fan. But
adding a simple 100R resistor to lover fan voltage reduces noise level from 31dB to 7dB.
!!!This modification is easy to perform but if you are not experienced you'd better not do it. During this tests I have broken supporting leg and the scope, but cyanoacrylate adhesive works excellent