230222 Radiated Immunity Pre-compliance Test

Hello everyone, welcome to Mach1 Design EMC channel.
Last time we talked about how to set up a radiated immunity test
using a very low cost antenna like this.
In the test setup, we injected high frequency noise into this antenna,
pointing this antenna to the DUT,
and we created some immunity failures of a product.
Another very popular immunity test is what we call Bow Current Injection Method.
In a way, Bow Current Injection Method, also known as the BCI test,
is very similar to a radiated immunity test using an antenna.
The methodology is very similar.
You still need pretty much the same setup as the setup we did last time.
However, rather than using an antenna, we can use a current clamp
and put the current clamp on the cable.
By doing so, we injected high frequency noise directly on the cable to create some noise,
hopefully to see if the unit can withstand the noise.
In today's session, we are going to look at how to set up a BCI test
using a very simple low cost setup to reproduce some of the immunity failures
we've seen in a proper EMC test lab.
Let's start.
Here's the setup.
As you can see, pretty much the same as last time.
We have a DUT, which we covered for confidentiality reasons.
We have a current clamp, same as last time.
Frequency bands up to 800 MHz to pick up the RF noise on the cable.
This is a current clamp, a homemade current clamp.
As you can see, in terms of size, it is much bigger than this commercial one.
The reason for that is the commercial one is really designed to pick up noise
rather than injecting noise.
To inject noise, you have to make sure that the core, like this, is big enough
so the core is not saturated.
And the making of this injection probe is actually very easy and simple.
You can find all the details on my website.
There's an article talking about it.
But just on the look at it, it's just seven or eight turns of cables
going through this ferrite core.
The core type is 28 material from Laird, I believe.
And then you have something like a connector like this.
And then, yeah, you power it up or driven by the same RF amplifier,
Techbox TBMDA3, which is capable of frequency range between 10 MHz and 1 GHz.
Difference with last time, as you can see here,
we are actually driving the RF amplifier using a function generator.
The reason being is that last time people asked,
oh, can I use a function generator to do the job?
And I said, of course you can.
But the trick is you need to set up the amplitude of the signal to be the right level.
Otherwise, any level higher than the rated 3 dBm would potentially damage this device.
So for instance, in this case, I'm injecting a sinusoidal waveform
with the peak-to-peak voltage of 600 mV.
And I am doing a sweep, basically sweeping from 100 MHz to 200 MHz.
And the other channel, I'm connecting to the oscilloscope.
As you can see, it's 600 mV peak-to-peak.
Make sure that you don't inject any signal larger than this.
And then it's sweeping between 100 MHz and 200 MHz.
Here again, very similar.
We have the listen, we have the power supply unit,
and we have a monitor to monitor the flow rate.
Because now we haven't turned the unit on, so it's still zero.
Another thing I want to mention is for this test,
I have a few ferrite cores clamped to this cable.
The reason being is that you don't want noise to go this direction,
so as to affect your reading.
We really wanted to see how noise has an impact on the DUT cell
rather than on this device here.
So we often put many ferrite cores,
make sure that the ferrite cores work in different frequency range.
So in this case, for instance, this is a 3.1 material,
this is 6.1 material, this is 4.4 material.
They work in different frequency range.
So any noise potentially travel on in this direction will be reflected back.
So what we measure is really the RF noise goes into the unit itself.
So without further ado, let's start.
First, we start the device on the test.
As you can see, now we see flow reading working normally, you know.
And then the minute I turn on the amplifier,
as you can see, the flow rate jumps to a very high level,
which is abnormal, and then you have the overflow error.
So that clearly indicates this unit has some immunity issue
in a frequency range of 100 MHz and 200 MHz at least.
And let's have a closer look at what we see here.
Here, as you can see, in order to protect the RF input of the spectrum analyzer,
I put a 20 dB attenuator.
And as you can see here, we are measuring the noise.
And you can see clearly the noise starting from 100 MHz
and slowly die off to the end.
Here is a little bit harmonics of the signal we created.
So we can see that the highest level is about 87 or let's say 80 dB microvolts.
This test setup is very neat in the sense that 20 dB attenuator,
then we have 20 dB ohm roughly of this current probe.
So what you read here actually is roughly the value of the current we've seen.
So in this sense, 80 dB microamps.
The calculation is simple.
You got 80 dB microvolts reading from here,
but you need to add 20 dB attenuator effect.
So that's 100 dB microvolts reading, let's just say.
But then again, this current probe has 20 dB ohm.
So minus 20 dB ohm, you get 80.
So that's why this setup is quite neat.
What we see here roughly is the RF current measured on the cable.
You can clearly see everything going on here.
Of course, the oscilloscope in this case is just to make sure that you monitor the input
to your RF amplifier, make sure that what you get to the RF amplifier
not exceeds the rated power, which is 3 dBm maximum.
So as you can see, I set the peak-to-peak voltage to be 600 millivolts.
Make sure the RF input of this unit is well protected.
And I think that's everything.
Okay, so in summary, to set up a low-cost BCI test in your workplace,
you really just need a few things,
which is a homemade buck current injection probe,
an RF amplifier, which is capable of injecting noise in the frequency range of interest,
and a spectral analyzer to monitor the RF current on the cable.
And that's it.
There are a few remarks on this test method.
First is, as you can see, the maximum RF current we can inject is about,
I would say, 80 to 90 dB microamps,
which is often sufficient enough for a pre-compliance BCI test.
The other thing is the Techbox RF amplifier we use,
you make sure that the RF input needs to be protected.
So if you're using a function generator like we did this time,
make sure that the amplitude of the signal you inject should be within the limit.
So in this case, 600 millivolts peak-to-peak, don't exceed that.
And yeah, once we recreate or we reproduce the failure
that we have seen in the proper test setup,
then we can use our magic to fix the product.
So in this case, actually, we have another sample where we fix the problem,
we put it back in, we do exactly the same test,
and the problem just got the reading just absolutely perfect without any issue,
even we injected a high-frequency noise on the line.
So if you like this video, please subscribe to my channel
or share it with your colleagues, and thank you for watching.
Thanks.