Knowledge Base

PCWI Porosity / Holiday Detector Models compared - Video

 

The video below provides you with a handy rundown of the types of detectors, how they differ and how they can be used.

 

 

Visit our Porosity product page for more information about our porosity detectors and accessories

 

Here's the video transcript for those who prefer to read

PCWI Detector model differences. The instruments and support that you need for your industry. This is about the PCWI detectors and the differences between the models. 

Range of porosity detectors, holiday detectors, and brushware

As you can see, we have got a range here of detectors and a vast range of brushware that is available. We have a wet sponge unit and 2 high voltage units. The 2 high voltage units are quite different to each other.

But let’s start with the wet sponge.

This is basically the layout: a small detector with various voltages and a sponge on an extendable handle that is wet and then applied to the surface. It is a little handheld unit with digital voltages displayed. As you can see there is 9v, 67.5 and 90v. This is very different this is a low voltage tester, very, very, and different to the high voltage testers. As you can see the extendable handle stretches out to 1.25mtrs.

large_replacement_sponge_head

You can see the brushware or sponge I suppose I should say. You have round sponges, I mean you can virtually make any sponge do anything. You need to keep in mind that the sponge must be wet for this to work so it wets the surface. It is not a dry test it is a wet test somewhere between wet and damp. It will only find a flaw which has actually got bare metal in the substrate. So if you have some deep scores and scars in the paint this isn’t most certainly is not going to find them. It will work on very thin coatings. Once again it needs a bare spot of substrate in the pinhole or scratch in order for it to find it as a flaw. So should it be used in heavy duty industrial coatings? No. I think with the advances in DC High Voltage testing - maybe you should look there.

high_voltage_detector_units

So, the 2 high voltage detectors you have a pulsed DC and a DC unit. DC stands for direct current and the DC unit is constant current so the current is there the volt is there and it is applied all the time.

detector_waveform

When you look at the pulse compared to the DC as you can see, the DC is a constant line, constant current that is applied to the surface. It is like having a bit of string tied both ends.  Whereas the pulse detector wave form, as you can see, the pulse to pulses, the drop to negative and then you can see the peak that is not there for long. This is probably somewhere between 26 to 30 something pulses a second so it is critical as to how fast you move with this as to whether you are going to skip over a flaw or a small pinhole or something like that. So let’s look at the DC 15.

Now, the DC 15 is a constant current/direct current unit and the voltage is displayed in the digital display. That is the applied voltage that is shown, so realistically it is no good to having a crest meter as such built into this because if something goes wrong with the display the crest meter is wrong as well. So there is no way of knowing.The volt voltage and the sensitivity can be adjusted and the alarm sensitivity. As you can see this is a fairly reasonably simple operation. There is an on and off test to make sure it is working correctly. With that once again I will go over the voltage. As you can see the DC is constant DC/constant current and the pulse, the pulse you can see the pulse is up there on the pulse unit.

dc_detector_high_voltage_concept

This here shows you the direct current/constant current flow. As you can see this is constantly on the move, there is no breaks unless you lift the handle or the brush off the surface of course, then that will stop: There will be no more current flowing. Of course, the more conductivity the coating has and the more contamination on the surface - like I said it is like a piece of string that is tied both ends. The more you pull on it the more voltage you pull down.

The superior way of testing in my belief but it does have some downfall if it comes to wet, damp, contaminated surfaces where a pulse would be better but for 99.9% of the jobs, I prefer the CDC as you can use it on thinner coatings right down to 150 microns or 250 microns, it just depends on you doing a few simple tests to make sure that you are not going to wind up burning anything through.

With that we move onto the pulse. It comes in a 20 and 40. As you can see, the coil on the handle the voltage is reduced there. You have the low voltage side which is the black lead. You might run to about 400 volts or something like that and then it is multiplied by 100 to 1 where you have got all this voltage is produced in the handle.

This is the layout as you can see, it is electronically up and down, and on and off. This is the pulse P20 and P40 which is actually a 20,000 and 40,000 volt.

We will look at this pulse again here versus the DC.

detector_waveform_pulse_dc 

As you can see the peak is not there all along and that is why it is cut virtually the slight chopping. The DC voltage, it does some have some negative part of it so if you are using it on a coating that builds up voltage static, there is some discharging of that coating as you move through, hence it works better on some coatings then a DC will especially carbonised rubber for instance - you won’t get a DC unit to work on carbonised rubber where as a pulse DC unit will.

dc_pulse_detector_concept

As you can see here the pulses are all broken up and you know it is in sections. There is 28 or so per second pulses so the minute you lift the probe off the surface this pulsing loads the pulses but the flow stops. As I said the pulse DC contains both positive and some negative charge, so charging of the surface and some discharging of the item under test.

So here we have a vast array of brushes and we can make brushes to suit any job. Specials are made to order but a lot of brushware is carried in stock. 

 

Visit our Porosity product page for more information about our porosity detectors and accessories

 

 

Categories: Videos