Electromagnetic Intereference

1) Are you sure that these are the EM radiations that are creating the temperature difference and not the heat generation by the equipments (say the spectrometer are generating too much heat ? )

2) It is perfectly possible that the temperature sensors of the AC are absorbing the EM radiations in case it is not correctly reported by your spectro people and that may be causing the ACs to assume the temperature more than it actually is and that is causing the malfunction.

All the radiations that are emitted may not be harmful, and hence may not violate the CE Norms but still work to malfunction AC (say Infra Reds ) and that same thing may even cause your basic premises (that there is a temperature differential) wrong since even in no differential it will show a differential.

Did you check the temperature at the individual AC output points (cold air temp ?)

Just a thought did you try to equalize the room temp by a fan or something like that ? agitators are regularly used in a lot of our ovens for this purpose.

Both may be correct but not compatble. In case it is the sensor problem, you can always have some EM shielding of the sensor. But first ensure that your sensors are reading correctly.

Just to give you one example again, in one of our oven, a few of the RTDs were exposed and were heated up by the heating coils and they were not reading the air temperature and rather the other tempeartuer. And when the temp of the oven as per instrumentation was 175 deg C, actual job was not even 100 (checked once physically) and we had to re-design the pick-ups.

Not enough information to make a definite diagnosis, but here are some thoughts to help troubleshoot.

First check the thermal issues as addressed by sb. If it isn't a thermal problem, then read on.

There are two ways the spectrometers can interfere electromagnetically with the ac units.

Either by radiation, or conduction.

In order for conduction to work, they have to share the same conductors, which likely means the feed from the ac mains. Do these devices share the same power source? If not, it isn't conduction. If they share the same feed, then check the power quality for the ac units when the spectrometers are not operating, and when they are, using an oscilloscope. If you see a big difference, you may have to provide different feeds.

If conduction isn't the problem, then look at radiation. The weak link on the ac is the temperature sensor, and especially the cable that runs between the sensor and the device which reads the temperature. If that cable is long, it can act as an efficient pickup.

Look for crosstalk, which could occur if a cable associated with the spectrometer runs parallel and close to the temp sense cable. If that is suspected, separate the cables to see if the problem is ameliorated.

If it isn't crosstalk, it could be ac mains return currents flowing on the temp sensor cable shield (assuming it is shielded). If the shield is grounded at both ends, this can happen. If you have a means of measuring low-levels of current, such as with a clamp-on ac ammeter, measure current on the temp sensor cable with spectrometers idle and then running. if you see a big difference, try lifting the shield at one end, to remove the ground loop. Be aware that when you do this, you are increasing susceptibility to radio frequency (rf) fields. If lifting a ground works for you, and then you have an rf problem, get back to me and I will tell you how to fix that as well.

It is highly unlikely that the spectrometers are causing rfi because they don't meet EMI requirements required for the CE sticker. The rf emissions requirements (EN 55022) are placed to protect broadcast band (BCB) radio reception, not ac units, even ac units with thermocouple sensors.

If the ac units are susceptible to low levels of rf (below one Volt per meter from 80 MHz to 1 GHz, and below 1 Volt of injected rf on the cable itself from 0.15 - 80 MHz), then the problem is with the ac units - they are supposed to meet these levels as a minimum if they sport a CE sticker. And these levels are orders of magnitude larger than what might incidentally be radiated from the spectrometer, even if it doesn't have a CE sticker: you cannot accidentally radiate at 1 Volt per meter at any distance other than cable-to-cable crosstalk: that requires an intentional source of rf at a level above 1 mW, and that doesn't happen by accident.

As I said to begin with, these are only very general guidelines. With feedback on the results of the suggested measurements, we may be able to pinpoint the problem.

Good Luck!

Is your ac compressor motor alone trips while spectrometer is working or total system is off - which you have not indicated.

Please Note and carry out all said modifications with total system Isolated from the Live supply.

Solutions are : I. Assuming only compressor tripping due EMI/RFI to electronic control of AC SYSTEM

1. Ensure firm earthing of AC control unit Box(Electronics)

2. Provide EMI / RFI SUPRESSORS in the input of the ac circuit for rating please consult your ac service engineers.

3 . you can shield the electronics control box of ac system with Magnetic shield foils available from electrical hardware stores if it is not available you can use silver foil paper used for packing hot food, but it should not have any gap between foils, and earth the total unit firmly.

II. Total AC system shuts off while Spectrometer is working

1.Check common electrical earthing system of your electrical supply.

2.Find out any imbalance load caused by the instruments and ac plant.

3. Any loose contacts/ switch contacts oxidised.

4. Ensure cable connected to the ac plant and spectro meter is good check terminations for proper contact and oxidisation.

Hope my suggestions will solve your problems.

Nagesh

Hi,

I am unfamiliar with the units you describe. As has been said EM interference may not be the issue, but check that both units have power line ground on their cases (if they have metal cases). The cases would act as EMI shields. If you have conducted interference, then line filters may help. If the problem is magnetic fields, then a steel plate between the two would help. MU-metal would be better. I doubt if that is the problem, though. If the units have plastic cases, then an aluminum plate tied to earth ground between the two may shield the EM. good luck.

-S

Hi guys,

does anyone here interest buying diffraction grating? Our company is on sale.

Please feel free to ask any questions that you may have or you can visit our website, www.optispac.com