Questions & Answers
Regarding the AN-1003 Anemometry system

 

Common CTA* Questions and Answers:
(*CCA=Constant Current Anemometry)


How do I measure the DC offset?

In order to operate the DC offset measurement, you need to press OPERATE + REFERENCE simultaneously.


I'm using a hot film in non-distilled water. After few days of continuous working the calibration drifts. What may be the problem?

Drift effects are caused by few major reasons:
         1. Air bubbles that are created by the heat of the probe and air in the water.
         2. Organic elements (as sea weeds etc.) which stick to the probe.
         3. Corrosion of the probe's wire.
         4. Salt or other minerals in the water.
         5. The PH of the water is not 7.0.
         6. The temperature of the water increases during the experiment due to the energy generated by the pump/motor.


When the "x2" resistance position is used, only five bridges can be operated in the mainframe. With the sixth bridge being operated, the power supply unit seems to be overloaded.

If you work with 6-10 channels at simultaneously 1:1 or 1:2 OHR, you need to use option 10 - High current power supply.


The noise level at the TOB seems to be higher on channels with option 04 (500 KHz) by about factor of 4-5.

The noise level is higher because of the bandwidth. If you trim the "Damping" trimpot and the tunning coil to a lower frequency response, you will notice that the noise level is reduced.


I have a vorticity sensor where every 4 sensors are connected to a common prong. Can I use it with the AN-1003?

Yes, you can do that. However, you must use a low OHR and you must connect the common prong to one BNC ground at the AN-1003 and use a very wide conductor (a silver strip is the best).


My wind tunnel's temperature is drifting in about 2 degrees Centigrade over 10 hours. How do I compensate this drift?

You should measure the Temperature changes using a Thermocouple (with the GAGE4000 unit or another digital thermometer) or with another channel which contains option 11 (CCA). After measuring the TOB voltage together with the Temperature, you should use a compensation equation for getting the "compensated" voltage. Please consult the factory for literature about temperature compensation.


I have some problems with the adjustment of the cable resistance: I cannot null a resistance of 0.5 Ohms in some of the bridge
ratios. How can I fix that?

The NULL trimpot is capable of zeroing cable resistance of 0.2 to 1.2 Ohms in any bridge ratio. The problem that you describe is due to change in the calibration of the channel. This calibration may be done by the user by using 2 external resistors only. Please consult the factory for calibration instructions.


I have an old instrument (8-12 years) and I've got some problems with the resistance decades in some of the channels:
When I move the thumblewheel switches a little bit, the resistance is changed and the TOB voltage changes/drifts. What to do?

The problem that you describe is due to bad contacts, which might be caused by many reasons. The way to fix it is by cleaning the resistance decades (inside) by Alcohol or Gasoline. Please consult the factory for cleaning instructions. You may also replace them at a low cost.


Common CCA* Questions and Answers:
(*CCA=Constant Current Anemometry)

Can I work with an old AN-1003 mainframe (more than 8 years old) and new CCA channels?

The new CCA channels cannot work with an old mainframe, from few reasons:
   The CCA monitoring output is shorted to another signal.
   The connector size might not be the same on both systems (and this may destroy your channels).
Please consult the manufacturer about your mainframe model and upgrading it.


I see a lot of 60, 120, 180 Hz noise on my CCA signal. What's wrong? (50, 100, 150 Hz. for Europe and Asia).

The 60 Hz signal that you see (in any anemometer) in CCA mode (only!!!) and its harmonics (120Hz, 180Hz. etc. ) are caused by the physical nature of the CCA circuit. The CCA does not have a feedback loop (like CTA) which cancels all such noises. It is actually very similar to an antenna amplifier (a current source that feeds the "Antenna" and a voltage amplifier).
Therefore, it collects all the noises from the environment (including 60 Hz. of course) and high frequency noises as well.


Solution:
    1) Take the probe cable away from any transformers, motors etc.
    2) Use a new cable with good shielding (also try magnetic shielding).
    3) Remove and transfer the internal power supply to a separate mainframe, by using the Opt. 13 power supply ext. mounting kit .       

    4) Try to ground one side of the cable to an "Earth" ground.


There is a "drift" of 0.3 V at the CCA channels during 24 Hours. Is this O.K.?

   Consider the sensitivity of your CCA channel - it depends on the sensor current, sensor's "Alfa"(Temp.Coef.), Gain etc. Check what TEMPERATURE SCALE you are using - it could be that 0.3V is equal to 0.01deg.C, in some cases. Check the drift and accuracy parameters of your thermocouple and reference instrument, and the temperature change of the probe and it's cable.
Usually, there is no noticeable drift in CCA (if the temperature is constant).


I use my CTA circuit to measure Temperature. I am trying to work at an OHR of 1.01 and measure temperature. Why do I get sensitivity to velocity?
  About working with OHR of 1.01: in theory it is possible, but it is not accurate. Use it only if you have no other choice. The velocity
sensitivity that you got is because you had some error in the adjustment of the sensor or cable resistance. Try to do it again or try OHR of 1.00 or even 0.99 (to compensate for the adjustment errors).


Sometimes the digital voltmeter and the channel output on the test module goes to "0 V" while having the channel under test,although the operation mode of this channel should provide a voltage different from zero. This state vanishes only by pressing some arbitrary function switches several times.

The problems is not with the test module switches. It might be because of bad contacts to the bus board. Please remove the test module and clean it's gold contacts by a piece of a rubber eraser. Then insert it back and the problem will be solved.

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