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Old November 7th, 2018, 07:25 PM   #1
NetNathan
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10 VDC to 0.250 VDC bridge

I want to accurately convert 0-10VDC to 0-250mV.
My device is 0-10 VDC out and the input module max is temperature or 250mV.
Would a resistance bridge work here to convert the 0-10VDC to 0-250mV?
Resistor sizes?
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Old November 7th, 2018, 07:37 PM   #2
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You don't need a bridge just a resistor divider depending on the output load
we would need to know the output load to calculate the resistor values
or you could use an op-amp set up as attenuator this would be less load dependent.

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Old November 8th, 2018, 11:26 AM   #3
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That's a big jump. Any reason you can't use something that will take the 0-10VDC?
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Old November 8th, 2018, 12:14 PM   #4
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That's a big jump. Any reason you can't use something that will take the 0-10VDC?
The module I am connecting is a remote TC module (Red Lion EtherTRAK2) It supports all TCs and up to 250mV, and I have (2) spare inputs available.
I do not really want to add an additional 4pt analog input module for (1) 0-10V signal.
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Old November 8th, 2018, 01:13 PM   #5
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ATC input would be a high impedance input so it would have little loading effect.
you could use a resistor divider network but you would be better off just adding an analog input module. then you would be sure of the accuracy of your readings
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Old November 8th, 2018, 01:33 PM   #6
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I've seen a lot of different signal converters over the years, but I have not seen one with a millivolt output. Someone probably makes one...but some searching didn't turn up anything.

Wilkerson Instruments or Omega might be worth contacting to see if they can help.
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Old November 8th, 2018, 01:39 PM   #7
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Quote:
Originally Posted by OkiePC View Post
I've seen a lot of different signal converters over the years, but I have not seen one with a millivolt output. Someone probably makes one...but some searching didn't turn up anything.
Someone asked for dual output thermocouple temperature transmitter on another forum and my response was that it's a big world out there and it might available, but I hadn't seen one yet.

Someone dug one up, with Australian URL.

It never ceases to amaze me what tiny market segments are addressed by some black box.

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Old November 8th, 2018, 05:45 PM   #8
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if you use the voltage divider network, you will need military grade resistors.
you will also need to do a lot of solder prep work and good solder techniques.
allied electronics is who we bought our last set pf precision resistors from.
there may be others.
Note I am not promoting allied electronics or associated with them, just giving the name of a vendor I used.

james
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Old November 8th, 2018, 06:31 PM   #9
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I would think the amount of time you're going to spend creating something that will give you the precision that will be needed to get anything close to an accurate reading would be offset by purchasing an analog module that will accept 0 to 10VDC however that doesn't take into account the "building it is most of the fun" aspect but if this is for a working automation application I (personally) would be much more comfortable with a standard solution rather than a custom one. It would also be much easier to deal with if a repair or replacement is needed down the road. Having said that, I would also think that such a custom built device would be difficult to properly protect from damage but I'm not an Electronics Engineer so I don't really know that one.
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Old November 9th, 2018, 05:33 PM   #10
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I will have to custom order the resistors to get an accurate voltage divider, so on to analog input field module.
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Old November 10th, 2018, 07:04 PM   #11
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the idea is simple, yes few resistors and a potmeter to make adjustments will work, however a TC input has a calculation to give direct temperatures out, with a slope that is not straight, so it will not be precise.
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Old November 10th, 2018, 07:32 PM   #12
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Quote:
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the idea is simple, yes few resistors and a potmeter to make adjustments will work, however a TC input has a calculation to give direct temperatures out, with a slope that is not straight, so it will not be precise.
+1 This must be considered in a case like this.

But in this particular case, according to the manual (for EtherTRAK 2 TC module), you can configure the inputs as mV instead of TC (+-250mV), which would give a linear response.
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Old November 11th, 2018, 11:45 PM   #13
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+1 This must be considered in a case like this.

But in this particular case, according to the manual (for EtherTRAK 2 TC module), you can configure the inputs as mV instead of TC (+-250mV), which would give a linear response.
Thee you go... I want use an input that is configured for +/- 250mv for 0-10V.
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Old November 12th, 2018, 01:58 PM   #14
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I will have to custom order the resistors to get an accurate voltage divider, so on to analog input field module.
You want to use one resistor, close to the ideal value and a pot (potentiometer) to make the adjustment for the other resistor in series. Then you don't need to wait for precision resistors.
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Old November 12th, 2018, 02:42 PM   #15
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You'll also have to make sure this is protected extremely well from noise. At voltages that low, even the smallest amount of noise on the line will have a nasty affect on the accuracy.
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