Bias_T and inductor resistance

[camerart]

Hi,
I have some circuits with possibly Capacitors, or inductors.
If I put an Ohm meter across a capacitor it should show nothing, but what should happen with the inductor?
Camerart

 

[Harald Kapp]

The Ohm meter will show the resistive part of the inductor, the resistance of the copper windings. Typically a low value, down to a few mΩ for good inductors. You may will have to take a 4-wire measurement to read such low values.

 

[camerart]

The Ohm meter will show the resistive part of the inductor, the resistance of the copper windings. Typically a low value, down to a few mΩ for good inductors. You may will have to take a 4-wire measurement to read such low values.

Hi H,
At this moment I only need to differentiate between Caps and Inductors, so a simple resistive test will do.
Later, I would like to understand more about filter, so will return.
Thanks.
C

 

[Harald Kapp]

When you want to use the inductors for filtering purposes, you need to know the inductance. That'll require an inductance meter.

 

[camerart]

When you want to use the inductors for filtering purposes, you need to know the inductance. That'll require an inductance meter.

Hi H,
I'm on the look out for one, but I've seen a big range of prices.
I've seen a tweezer type small one, which will do for my skills, can you suggest one app £50-100, please?
C

 

[Harald Kapp]

I have one similar to this one.
Not a precision instrument, but a nice gimmick to identify a range of components.
I'll have to admit, however, that I never used it on inductors. The ad states 0.01 mH ... 20 H which is good if the instrument holds up to the promise.

 

[camerart]

I have one similar to this one.
Not a precision instrument, but a nice gimmick to identify a range of components.
I'll have to admit, however, that I never used it on inductors. The ad states 0.01 mH ... 20 H which is good if the instrument holds up to the promise.

Hi H,
I've tried the cheaper ones, and they do work for the price, but I think I will look for one a bit more in the hope that it's better.
Thanks, C

 

[Delta Prime]

If I put an Ohm meter across a capacitor it should show nothing, but what should happen with the inductor?
Camerart

Well yes and no.
A faulty capacitor may be"open"when measured with a multimeter, & a good capacitor will also test "open."
You can test capacitors in-circuit for short-circuits.With an analog meter use the x1 ohms range.
To test a capacitor for leakage, you need to remove it or at least one lead must be removed.
Use the x10k range on an analogue or digital multimeter.
For values above 1uF you can determine if the capacitor is charging by using an analogue meter.
The needle will initially move across the scale to indicate the cap is charging,then go to "no deflection."
Any permanent deflection of the needle will indicate leakage.
You can reverse the probes to see if the needle moves in the opposite direction.
This indicates it has been charged. Values below 1uF will not respond to charging the needle will not deflect.
This does not work with a digital meter as the resistance range does not output any current & the electrolytic does not charge.
Coils, inductors, chokes & yokes are just coils (turns) of wire.The wire may be wrapped around a core made of iron or ferrite.
You can test this component for continuity between the ends of the winding and also make sure there
is no continuity between the winding & the core.
The winding can be less than one ohm, or greater than 100 ohms. A coil of wire is also called an inductor & it might look like a very simple component, but it can operate in a very complex way.
The quickest way to check an inductor is to replace it, but if you want to measure the inductance, you can us a inductance meter.You can then compare the inductance with a known good component.
The value of some inductors is very small & some Inductance Meters do not give an accurate reading.
The solution I use is to measure a larger inductor and note that reading. Now put the two inductors in series and the values add up - just like resistors in series.This way you can measure very small inductors.

 

[camerart]

Well yes and no.
A faulty capacitor may be"open"when measured with a multimeter, & a good capacitor will also test "open."
You can test capacitors in-circuit for short-circuits.With an analog meter use the x1 ohms range.
To test a capacitor for leakage, you need to remove it or at least one lead must be removed.
Use the x10k range on an analogue or digital multimeter.
For values above 1uF you can determine if the capacitor is charging by using an analogue meter.
The needle will initially move across the scale to indicate the cap is charging,then go to "no deflection."
Any permanent deflection of the needle will indicate leakage.
You can reverse the probes to see if the needle moves in the opposite direction.
This indicates it has been charged. Values below 1uF will not respond to charging the needle will not deflect.
This does not work with a digital meter as the resistance range does not output any current & the electrolytic does not charge.
Coils, inductors, chokes & yokes are just coils (turns) of wire.The wire may be wrapped around a core made of iron or ferrite.
You can test this component for continuity between the ends of the winding and also make sure there
is no continuity between the winding & the core.
The winding can be less than one ohm, or greater than 100 ohms. A coil of wire is also called an inductor & it might look like a very simple component, but it can operate in a very complex way.
The quickest way to check an inductor is to replace it, but if you want to measure the inductance, you can us a inductance meter.You can then compare the inductance with a known good component.
The value of some inductors is very small & some Inductance Meters do not give an accurate reading.
The solution I use is to measure a larger inductor and note that reading. Now put the two inductors in series and the values add up - just like resistors in series.This way you can measure very small inductors.

Hi D,
Thanks, for the explanation.
I'm going to get a proper meter, so any technical stuff will be read by that.
I only wanted to check between Caps and Inds on a pcb, today.
C

 

[kellys_eye]

can you suggest one app £50-100, please?

Here's one I swear by.....

All-in-1 LCD Component Tester Transistor Diode Capacitance ESR Meter Inductance | eBay

Find many great new & used options and get the best deals for All-in-1 LCD Component Tester Transistor Diode Capacitance ESR Meter Inductance at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

They are so good I have three of them (well, accidentally ordered too many!) but they have good reviews across the internet and at that price simply can't be beaten.

 

[camerart]

Here's one I swear by.....

All-in-1 LCD Component Tester Transistor Diode Capacitance ESR Meter Inductance | eBay

Find many great new & used options and get the best deals for All-in-1 LCD Component Tester Transistor Diode Capacitance ESR Meter Inductance at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

They are so good I have three of them (well, accidentally ordered too many!) but they have good reviews across the internet and at that price simply can't be beaten.

Hi K,
This looks like the one shown earler.
Thanks I'll consider it.
I'm looking for tweezer type, if possible.
C

 

[Bluejets]

Get yourself a $20 component tester......
https://www.ebay.com.au/itm/173534514262

 

[kellys_eye]

I'm looking for tweezer type, if possible.

Tweezer types are available - Elektor magazine are doing an offer on a multi-purpose tweezer measurement device:

Miniware DT71 Mini Digital Tweezers

LCR/ESR Meter, Multimeter, SMD Tester with built-in Micro Signal Generator The Miniware DT71 digital tweezers are a truly "smart" buy for pro engineers and makers alike. The compact DT71 has a unique trinary structure which can be separated into the controller, testing arms, and tweezer tips...

www.elektor.com

really only suitable for surface mount components though.

 

[camerart]

Tweezer types are available - Elektor magazine are doing an offer on a multi-purpose tweezer measurement device:

Miniware DT71 Mini Digital Tweezers

LCR/ESR Meter, Multimeter, SMD Tester with built-in Micro Signal Generator The Miniware DT71 digital tweezers are a truly "smart" buy for pro engineers and makers alike. The compact DT71 has a unique trinary structure which can be separated into the controller, testing arms, and tweezer tips...

www.elektor.com

really only suitable for surface mount components though.

Hi K,
Thaks, I want them for surface mount compnents, so these will be fine.
C

 

[crutschow]

This does not work with a digital meter as the resistance range does not output any current & the electrolytic does not charge.

Of course they do, as they generate a constant-current through the resistance being measured and measure the resulting voltage to determine the resistance.
How do you think digital meters measure resistance?

They don't work as well to measure a capacitor, since the meter reading update is relatively slow and does not smoothly follow the charging voltage as an analog meter does.

 

[Delta Prime]

They don't work as well to measure a capacitor, since the meter reading update is relatively slow and does not smoothly follow the charging voltage as an analog meter does

Sensei it's an honor!The man with clever circuits for All occasions.
You're all caught up in my quantum entanglement.

For values above 1uF you can determine if the capacitor is charging by using an analogue meter.
The needle will initially move across the scale to indicate the cap is charging,then go to "no deflection."
Any permanent deflection of the needle will indicate leakage.
You can reverse the probes to see if the needle moves in the opposite direction.
This indicates it has been charged. Values below 1uF will not respond to charging the needle will not deflect.
This does not work with a digital meter as the resistance range does not output any current & the electrolytic does not charge

It's okay sir. you are allowed!

 

[davenn]

I only wanted to check between Caps and Inds on a pcb, today.

visually, that is usually pretty easy

 

[camerart]

Hi,
I've just bought some component measuring tweezers.
They look ok, but they aren't able to read uH inductors, which I need to do.
How can I check the values of uHinductros.
Camerart

 

[camerart]

Hi,
I've just posted another one, forgetting that this one is live!
Anyway, I bought the #14 ones, but now I find they can't read the small value inductors I need to read.
Is there a way I can read them, withought spending any more money?
C

 

[kellys_eye]

Multifunction measuring instruments all have limitations and devices dedicated to such 'individual' components tend to be far more accurate. For 'small' measurements this is particularly noticeable and inductors as well as capacitors are commonly notoriously difficult to measure using 'broadbased' test equipment like your tweezers.

One relatively easy method (assuming you have the facilities and equipment i.e. accurate frequency counter) is to make a small LC oscillator with a calibrated capacitance and add the inductance to it - thereafter apply the relevant formula to derive the 'C' as the factor.