Are there other types of RF loads?

[daisizhou]

Hi everyone

I noticed that many people test RF power using power resistors as loads to test the power supply.If you need power resistors of different resistance values, you will need a very bulky resistor box to hold them.Very bulky and difficult to transport when out and about.

Are there other types of loads that could replace them?

[wasedadoc]

RF or PSU loads?  Loads for DC PSUs can use wire wound resistors.  Wire wound resistors have inductance and may be quite unsuitable as RF loads.

I have been known to overrun a load resistor by immersing it in a container of reasonably pure cold water.

[joeqsmith]

For RF you would use something like:
https://btgstore.com/rfattenuators.html

[daisizhou]

RF or PSU loads?  Loads for DC PSUs can use wire wound resistors.  Wire wound resistors have inductance and may be quite unsuitable as RF loads.

I have been known to overrun a load resistor by immersing it in a container of reasonably pure cold water.

I mean for RF power,Frequency is about 500KHZ-800KHZ，Voltage is about 8kv-20kv。
Non-inductive wirewound resistor，Wirewound resistors are made using a special winding method and look very similar to ordinary resistors.

[fourfathom]

For RF you would use something like:
https://btgstore.com/rfattenuators.html

And using an open or short-circuit load on the attenuator to get loads greater and less than 50 Ohms.  Just do the math.  Example: a shorted 3dB attenuator gives you a 16.6 Ohm load.  An open 3dB attenuator gives a 150 Ohm load.  Check the attenuator power ratings.

[CaptDon]

Where on earth are you dealing with 8KV to 20KV into a dummy load and what impedance??? (20K x 20K) / 50 is a hell of a lot of power!!! What exactly are you doing? That's going to be some big resistors or a dump truck full of little ones. Your numbers seem a bit out to lunch.

[fourfathom]

Where on earth are you dealing with 8KV to 20KV into a dummy load and what impedance??? (20K x 20K) / 50 is a hell of a lot of power!!! What exactly are you doing? That's going to be some big resistors or a dump truck full of little ones. Your numbers seem a bit out to lunch.

Oh.  Hey, that's only 8 Megawatts. (WTF???)

[daisizhou]

Where on earth are you dealing with 8KV to 20KV into a dummy load and what impedance??? (20K x 20K) / 50 is a hell of a lot of power!!! What exactly are you doing? That's going to be some big resistors or a dump truck full of little ones. Your numbers seem a bit out to lunch.

I want to test the following hosts
https://www.perlong-china.com/PT300-PT300A-PT300B-H-F-Electrosurgical-Unit-pd6042484.html

[T3sl4co1l]

The load in that case isn't really resistive, it's a complex and variable impedance due to motion, arcing and flesh.  Would a cut of pork not demonstrate it more directly?

Tim

[daisizhou]

The load in that case isn't really resistive, it's a complex and variable impedance due to motion, arcing and flesh.  Would a cut of pork not demonstrate it more directly?

Tim

Objective measurement is needed, not rough measurement.I have FLUKE 8920A high-frequency voltmeter (RMS)，So I need a load

[coppercone2]

bro hire a consultant for that machine, its not some hobby antenna run out of a old shed

I would not even plug anything into that machine.

More then likely, return to company for service. Messing with something like that is how you go to jail with just a drop of bad luck.

[daisizhou]

 ;DDon't worry, this is a pet hospital device.It has only served animals and never worked on humans.

[vk4ffab]

Where on earth are you dealing with 8KV to 20KV into a dummy load and what impedance??? (20K x 20K) / 50 is a hell of a lot of power!!! What exactly are you doing? That's going to be some big resistors or a dump truck full of little ones. Your numbers seem a bit out to lunch.

Looking at his frequency range its no different to AM broadcast and those giant wire wound resistors is exactly what they use fr dummy loads. Banks of them in a cabinet with cooling with spares to match. He needs 500ohms that can deal with1kw a few big wire wounds would do that easy.

[vk4ffab]

;DDon't worry, this is a pet hospital device.It has only served animals and never worked on humans.

Those big wire wound resistors will work for what you are testing, the machine puts out 300 watts into 500 ohms, build a 500ohm dummyload that can sink 1000w and you will be golden, as long as you are aware of the inherent danger of those power levels and related voltages because high power RF hurts LOL ask me how I know.

If you cannot source them in China, you might be able to find high wattage flange mount RF resistors in the 200 to 400W range and mount them up on a suitable heatsink in series and parallel configuration to get close to the resistance you need with excess power rating. I built my dummyload using 4 200W 200 ohm flange mount resistors off ali express.

https://www.aliexpress.com/item/1005006901914907.html?spm=a2g0o.productlist.main.5.6d186y806y801D&algo_pvid=256c4d1f-f4a6-4365-a5b7-da281e7bafb1&algo_exp_id=256c4d1f-f4a6-4365-a5b7-da281e7bafb1-2&pdp_npi=4%40dis%21AUD%2119.29%2119.29%21%21%2112.91%2112.91%21%402103080717250819045168173e8d87%2112000038662949312%21sea%21AU%210%21ABX&curPageLogUid=biTKTYIj90Oo&utparam-url=scene%3Asearch%7Cquery_from%3A

5 of these in series mounted on a giant heat sink would work fine.

[daisizhou]

;DDon't worry, this is a pet hospital device.It has only served animals and never worked on humans.

Those big wire wound resistors will work for what you are testing, the machine puts out 300 watts into 500 ohms, build a 500ohm dummyload that can sink 1000w and you will be golden, as long as you are aware of the inherent danger of those power levels and related voltages because high power RF hurts LOL ask me how I know.

If you cannot source them in China, you might be able to find high wattage flange mount RF resistors in the 200 to 400W range and mount them up on a suitable heatsink in series and parallel configuration to get close to the resistance you need with excess power rating. I built my dummyload using 4 200W 200 ohm flange mount resistors off ali express.

https://www.aliexpress.com/item/1005006901914907.html?spm=a2g0o.productlist.main.5.6d186y806y801D&algo_pvid=256c4d1f-f4a6-4365-a5b7-da281e7bafb1&algo_exp_id=256c4d1f-f4a6-4365-a5b7-da281e7bafb1-2&pdp_npi=4%40dis%21AUD%2119.29%2119.29%21%21%2112.91%2112.91%21%402103080717250819045168173e8d87%2112000038662949312%21sea%21AU%210%21ABX&curPageLogUid=biTKTYIj90Oo&utparam-url=scene%3Asearch%7Cquery_from%3A

5 of these in series mounted on a giant heat sink would work fine.

Thanks

I can purchase that type of resistor and get it.

I hope to find a better alternative item,Because those resistors are too large and inconvenient to carry around,Is there a better solution?

[CaptDon]

Here is some advice from a BioMed tech of a 900 bed hospital. An ESU generates specific waveforms based on task. Notice the machine can do several types of electro-surgical procedures. That machine looks like an exact knock-off of stuff I tested in 2005-2010 in the states. We had a specific testing device which probably cost as much as the ESU itself. We tested each function at probably 5 different power levels and the calibration tester gave a direct reading of power in watts. Notice also most of the specs are at 500 ohms but there is also a function to be tested at 100 ohms. A 225 watt (one of the standard sizes of ceramic resistors) 500 ohm resistor with the N.I. specification (non-inductive) could work for you since these units were meant for short bursts of use. But, to be on the safe side get a pair of 225W 1000 ohm N.I. resistors and parallel them for 500 ohms. A single 225 watt 100 ohm should be fine for the other mode. The waveform can be very strange and I am not sure how you expect to get a meaningful 'RMS power output' measurement unless the meter you use to measure the signal can do some amazing math functions.

[LM21]

There  is a special oil to cool high power loads. Transformer oil or something  similar. But  those are  not hobby projects
Radio stations have them

[CaptDon]

Don't get too crazy with exotic dummy loads. As I stated, the ESU's are used intermittantly in surgery and you really only need to activate it long enough to get a meaningful power output indication. You're not cutting a cow in half or seaming two halves back together. Your kit needs only exactly what I stated, a pair of 1000 ohm resistors in parallel, 225 watts each, standard size AND a single 225 watt 100 ohm resistor. Again, I am not sure your true RMS meter will give a valid result but may be close enough for power verification within about 10% which should be fine. No need to overthink the dummy load. You really should think about purchasing a 'real' ESU tester / calibrator. If you do proceed with the RMS voltmeter you should do a data entry spread sheet or a chart that shows RMS power vs. voltage at 500 ohms and at 100 ohms.

[daisizhou]

Don't get too crazy with exotic dummy loads. As I stated, the ESU's are used intermittantly in surgery and you really only need to activate it long enough to get a meaningful power output indication. You're not cutting a cow in half or seaming two halves back together. Your kit needs only exactly what I stated, a pair of 1000 ohm resistors in parallel, 225 watts each, standard size AND a single 225 watt 100 ohm resistor. Again, I am not sure your true RMS meter will give a valid result but may be close enough for power verification within about 10% which should be fine. No need to overthink the dummy load. You really should think about purchasing a 'real' ESU tester / calibrator. If you do proceed with the RMS voltmeter you should do a data entry spread sheet or a chart that shows RMS power vs. voltage at 500 ohms and at 100 ohms.

Thanks

http://www.metek.com.tr/main/web/urunresim/ESUComparisonChart.pdf
I was lucky enough to find the link above.

As far as I know, the latest model is Fluke QA-ES III。But it looks no different than QA-ES II,In terms of function, a frequency display has been added, that's all.

In my opinion,The above wire-wound resistors are used as loads in 454a, FLUKE QA-ESII, and QA-ESIII hosts.This makes all the hosts too bulky and inconvenient to carry.

I wonder if there is a better loadout to replace them completely

[abeyer]

You're not cutting a cow in half

That sounds like a challenge

[boB]

Fans cool down power resistors pretty well.

[Robert763]

I'd Use two 1K Arcol FPA350 resistors on a small fan cooled heatsink. Connect them in parallel for 500 ohms.
If you need to check at 100 ohms add a extra 100 ohm one.

https://www.farnell.com/datasheets/2572861.pdf

[daisizhou]

I'd Use two 1K Arcol FPA350 resistors on a small fan cooled heatsink. Connect them in parallel for 500 ohms.
If you need to check at 100 ohms add a extra 100 ohm one.

https://www.farnell.com/datasheets/2572861.pdf

This thick film resistor looks good.But I am not sure whether it can be insulated for a long time under the 3kv withstand voltage.
Also, whether it can maintain stability during long-term operation and whether the consistency is the same.
Can the resistance value accuracy be controlled to 1%-2%?

[Randy222]

Where does kV come from? That unit puts out around 400vac at max output power. (400v 500ohm 0.78amp 300watt)

"500 ohms" in the specs for "load" is deceiving. And with the spec sheet, the unit is only around 37% efficient between input and output.

Is that resistive load (Rdc) or is that a Z spec? Take for example the large wirewound item for load, When the machine is running 330kHz you could have mostly inductance to present the machine a "500ohm" load as Z, but I bet ya the machine goes poof with full inductive load.

My guess is, there's little inductance or capacitance in what the tool end touches, the load is likely mostly Rdc. I would stay away from wirewound.

An alternative is a bucket of cold salt water, with electrode spacing just so to show 500 ohms. I am not 100% what salt water looks like in terms of the components of Z at 330kHz 430kHz and 1MHz. Perhaps using a VNA or the like to test the LCR at those frequencies.

[daisizhou]

NHL-175-07E is a special wirewound resistor with almost zero inductance at high frequencies.

Input signal:Frequency 400KHZ-850KHZ, Voltage:800kv-2500KV，Current: 0.05ma-0.5A Common resistance range 150 ohms-300 ohms