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Using A Hall Effect Sensor To Detect Voltages Present On Diferent Circuits "wir — Parallax Forums

Using A Hall Effect Sensor To Detect Voltages Present On Diferent Circuits "wir

beazleybubbeazleybub Posts: 102
edited 2008-06-30 04:22 in BASIC Stamp
I do not know much about hall effect sensors but wonder if anyone can help me decide how to approach using my BS2 to detect when a different·wires are live with DC voltage.

The circuit I would like to monitor operates on 30V DC. I bought optocouplers earlier but have found that for such a high voltage they seem to be impractical because I would need to use an 180 OHM 2 Watt resistor which is from what I have found are expensive and elusive.

I also find the optocoupler for my particular application useless because the device I am designing will be monitoring DC voltages ranging from 12V to 50V and this would require many different resistor configurations which makes marketing my device harder.

Would a hall effect sensor be a better choice for detecting a wider variety of DC voltages?
I'm not asking for programming help just what to use as a switch so my BS2 can see that a circuit is live with DC voltage. Thanks a bunch!

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What if there was nothing? Nothing is something!

Post Edited (beazleybub) : 6/27/2008 3:11:20 PM GMT

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-06-27 12:24
    OK, electromagnetism: you wrap a length of wire around a nail and run a DC-current through that wire --·Voilá, a magnet.·

    So, you propose to wrap a length of wire around a hall-effect sensor or wrap wire around an iron-core of some sort and a hall-effect sensor?

    [noparse][[/noparse] I disagree with your opto-coupler calculations, the LED shouldn't be running full-bore, it should be able to make it with 5mA, possibly less.· 30V, 5mA, approx. 5.6KΩ ]
  • Mike GreenMike Green Posts: 23,101
    edited 2008-06-27 14:00
    Most solid state relays use an optocoupler for their input circuitry and allow input voltages from 3 to 32V. For 12V at 5mA, you would have R = E / I = (12V-1.7V) / 5mA = 2K (roughly). At 50V, you'd have I = E / R = 50V / 2K = 25mA and you would need a 2W resistor for this voltage.

    You might be better off splitting the voltage range into two with one range being 3-35V and the other 30-50V with two series resistors and the tap used for the lower range. You'd be able to keep the power dissipation lower at the high end and the LED current.
  • beazleybubbeazleybub Posts: 102
    edited 2008-06-27 14:07
    electromagnetism: When current flows it produces a magnetic field which has a strength proportional to the current flowing.

    You would not need to wrap wire around anything just simply place the wire through the center of a current sensing hall effect sensor.

    As I am sure you are aware PJ Hall effect sensors come in many varietys including a current sensor.
    http://www.mouser.com/Search/ProductDetail.aspx?qs=UO2oIyMggj8BEQpE8RxNZQ%3d%3d

    Your right my calculations are not right. I was looking at the absolute maximum ratings. (Whoops)

    I still do not think that using an optocoupler is the best way to go for my particular application because my device will be used on varying voltages not just one set voltage. (12-50V)

    I guessed that the use of a current sensing hall effect sensor would be a good way to go but if you or anyone else has a better idea I'm listening attentively, besides the sensor I proposed is pricy at $16.33 each.

    Thanks


    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    What if there was nothing? Nothing is something!

    Post Edited (beazleybub) : 6/27/2008 3:10:38 PM GMT
  • beazleybubbeazleybub Posts: 102
    edited 2008-06-27 14:11
    Maybe it would help if i posted a link to my particular optiocoupler.

    http://www.vishay.com/docs/83503/tcet1100.pdf·I am using the tcet1100

    Thanks to both of you for helping me take a stab at this.tongue.gif

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    What if there was nothing? Nothing is something!

    Post Edited (beazleybub) : 7/1/2008 7:23:47 AM GMT
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2008-06-27 16:15
    beazleybub,


    For your model (TCE1100) The Current transfer ratio table uses a forward current value of 5mA for their test condition.

    Looking at Figure 7, 5mA places the forward Voltage of the OPTO-LED at about 1.1 Volts. This is good, Looking at Figure 10 and Figure 13, 5mA places you near the top of the linear operating region of the OPTO-LED

    If your input voltage range is from 12V to 50V, then I would select a current limiting resistor that would allow for 5mA at 50V.

    R = ( Vsource - Vled ) / Iled
    R = ( 50V - 1.1V ) / 5mA
    R = 48.9V / 5mA
    R = 9.7K ... rounding up to the closest standard is ok... So R = 10k

    TO determine Power....

    P = I * V
    P = 5mA * 50V
    P = 250mW.... So you need at least a 1/4 Watt 10K resistor

    By re-iterating the formula below at 12V and looking at Figure 7, your forward voltage should now be closer to 1V and your Collector current from Figure 10 still appears to be an approximate 1:1 ratio where your current transfer ratio seems to drop about 40% which is also good... <-- This is where you would/could optionally take an analog measurement through an ADC of some variety connected to your Stamp.

    To double check the low voltage range of 12V

    I = ( Vsource - Vled ) / Rled
    I = ( 12V - 1.0V ) / 10k
    I = 11.0V / 10k
    I = 1.1 mA

    And, to double check the high voltage range of 50V

    I = ( Vsource - Vled ) / Rled
    I = ( 50V - 1.1V ) / 10k
    I = 48.9V / 10k
    I = 4.89 mA

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • beazleybubbeazleybub Posts: 102
    edited 2008-06-27 16:19
    God bless you man. I really mean it! Now I can clear my browsers cache and rest my fingers.

    I would also like to thank Mike & PJ for the help!
    You guys are responsible for helping me learn something I will use for a lifetime.
    ·············································· roll.gif


    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    What if there was nothing? Nothing is something!

    Post Edited (beazleybub) : 6/27/2008 5:14:51 PM GMT
  • OptoDragonOptoDragon Posts: 3
    edited 2008-06-30 02:17
    Good Day...
    I'm interested in your project. I'm trying to design a connector pin tester. In the process I need to know if I have continuity between pins and/or shells - I don't want that! But that is one of the points that I'm checking for. I have a posting under "Connector Pin Tester". I work like to see what you doing.
    Thanks... OptoDragon...
    skull.gif
  • beazleybubbeazleybub Posts: 102
    edited 2008-06-30 04:22
    Wow, I'm flattered that you are interested in my project!
    But the truth is I do not know enough to confidently help you.
    I will try to answer any questions I can but my knowledge is limited.

    Just keep searching and asking questions. Someone out there will help you.
    People like Mike Green and PJA (not to mention parallax forum moderators) are very knowledgeable and care enough to try to help.

    Sometimes when you ask a question people will help you without giving you the exact answer you are looking for. But really this is good way to learn·because it will force you to dig deeper and think.


    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    What if there was nothing? Nothing is something!
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