Radiant Electronics X4 at less than 10mw, how accurate?

[Rifter]

The specs says 1mw min but 10mw recommended.

So if anyone who owns one wants to chime in and let me know how accurate it is under 10mw that would be great. Thanks.

I just ordered one anyways as it seems like a no brainer for the price point im just curious how it will perform under 10mw.

When it shows up in a few weeks and my glasses and my 2 lasers also show up ill do some testing and let you guys know how it goes, i have a 5mw and a 50mw laser on order.

 

[ARG]

The reason they recommend at least 10mW is that heat from anything (like a small breeze) will cause a milliwatt of inaccuracy or so. While this isn't a huge issue when measuring 1W of power 1mW of absolute inaccuracy means a 10% percentage uncertainty at 10mW.

 

[Rifter]

The reason they recommend at least 10mW is that heat from anything (like a small breeze) will cause a milliwatt of inaccuracy or so. While this isn't a huge issue when measuring 1W of power 1mW of absolute inaccuracy means a 10% percentage uncertainty at 10mW.

Would this be true for any LPM?

 

[ARG]

Would this be true for any LPM?

Any thermal based LPM (which is what almost everyone uses on the forums)

Even the Ophir 20C heads most people use here are only really rated for a 20mW minimum.

 

[Bionic-Badger]

Not necessarily. It depends on the sensor's characteristics. In this case, it's just a TEC attached to an IC heatsink. The lack of mass and large finned area may make the sensor more susceptible to ambient heat.

 

[busman2]

I tried to measure my Rigel5 593.5nm which was measured with a laser bee to average @ 4.7mW, however the radiant did not even detect it! If I get time this evening I will try again and will try and set it up a bit better.

 

[bdgreenb]

They say 10mw but it's closer to 30, which is the same amount of thermal capacity as a big breath. When you go low make sure all windows and doors are closed and refrain from breathing on or being close to the sensor.

 

[ScottW]

They say 10mw but it's closer to 30, which is the same amount of thermal capacity as a big breath.

As another example...

I just set my X4 up, zeroed it, then put my open palm about 2" in front of the sensor. I got a reading of 5.2mW.

So holding a low power laser in your hand (or having a breeze) could greatly affect the reading.

 

[Rifter]

How close can the laser be to the sensor? I can always build an enclosure for the sensor and tripod to eliminate environmental variables when testing lower powered lasers.

 

[ARG]

The manual recommends 30cm away IIRC.

Putting the sensor in an enclosure would be a bad idea, the sensor needs to be able to cool off when high powers are applied.

 

[Rifter]

The manual recommends 30cm away IIRC.

Putting the sensor in an enclosure would be a bad idea, the sensor needs to be able to cool off when high powers are applied.

That's why I said when testing low powered lasers, I would imagine anything over a few hundred mw's environmental variables would be irrelevant

 

[ScottW]

The manual says "20-30cm away from the sensor."

Some kind of temporary enclosure, just to eliminate drafts or other errant heat sources from affecting the reading, would be a good idea when measuring low-powered beams (say <100mW). And with very low powers, placing the sensor closer than 20cm (like 1-3cm) is beneficial.

For higher powers the ambient sources are unlikely to make a big difference, and as ARG said above, could be problematic if they prevented the TEC heat sink from cooling properly.

It is also really important to de-focus higher power lasers such that the "dot" is spread out on the TEC surface. Failure to do this can easily burn the TEC coating and damage the sensor.

 

[busman2]

I did get to do another test on the Rigal5 593.5nm. Because of its low output I also placed the sensor inside a tube, one of those thermal beer coolers! :beer: Also at 30cm the sensor is not even going to know that it was there so at 30mm I got a stable reading at 5.4mW which is somewhere around the mark. I think a "standard" anything will not give an accurate reading because low powered lasers are going to drop of in their thermal range very quickly and even quicker in a cold environment. For the higher powers it will also vary depending on how much out of focus you set the lens to, to much and the heat is dissipated over a wider area and even slightly off the sensing area, is every thermal sensor exactly at the same sensitivity over its entire area? There are a lot of variables here, from user to user, lpm to lpm and laser to laser. If you have some idea already what your laser is outputting then I think your off to a good start on how to read your lpm! Well for me that's seems to be the only way it's going to work but I am more than willing to hear others thoughts on this .

 

[ScottW]

Also at 30cm the sensor is not even going to know that it was there so at 30mm I got a stable reading at 5.4mW which is somewhere around the mark. I think a "standard" anything will not give an accurate reading because low powered lasers are going to drop of in their thermal range very quickly and even quicker in a cold environment. For the higher powers it will also vary depending on how much out of focus you set the lens to, to much and the heat is dissipated over a wider area and even slightly off the sensing area, is every thermal sensor exactly at the same sensitivity over its entire area? There are a lot of variables here, from user to user, lpm to lpm and laser to laser.

Agree with all that, busman2.

In particular... Distance from the X4's sensor (and I assume most thermopile/TEC sensors) will make a significant difference on low-powered lasers. Although the manual says "20-30cm", I agree that a shorter distance (even 1-3cm) is more appropriate for very low power devices.

Example: I just measured a little Aixiz 635nm 5mW 8x31 module on the X4; at 20cm it read about 2.3mW, while at 2cm it read 5.3mW). That sort of difference is pretty meaningless on a 3W measurement, but represents a huge magnitude error on 5mW.

 

[Rifter]

Agree with all that, busman2.

In particular... Distance from the X4's sensor (and I assume most thermopile/TEC sensors) will make a significant difference on low-powered lasers. Although the manual says "20-30cm", I agree that a shorter distance (even 1-3cm) is more appropriate for very low power devices.

Example: I just measured a little Aixiz 635nm 5mW 8x31 module on the X4; at 20cm it read about 2.3mW, while at 2cm it read 5.3mW). That sort of difference is pretty meaningless on a 3W measurement, but represents a huge magnitude error on 5mW.

Good to know so even a small enclosed box with the heatsink and tri pod right beside each other should work to measure less than 50mw units?

 

[ScottW]

Good to know so even a small enclosed box with the heatsink and tri pod right beside each other should work to measure less than 50mw units?

I would think so.

The X4 *seems* to be accurate enough at the 5mW level as long as extraneous heat/cooling sources are kept away. But I'm just basing that on the assumption that Aixiz module is ~5mW as advertised (the X4 measured it at 5.3mW). I don't have any way to actually validate its accuracy at that power level, as I have neither a "known, LPM'd <5mW" laser, nor another more sophisticated LPM intended for low power measurements to check it against.