Power Meters FAQ's

Thermal Laser Power Sensors

Using Your Sensor

06/09/14

Thermal sensors for intermittent use such as models 30(150)A, L40(150)A etc. can be used up to the powers in parenthesis for a period given approximately by the following formula: The rule of thumb is that you can use the sensor for 1 minute/watt/cm3 of sensor. So for 150 watts for 30(150)A you have 1minute*165cm3/150watt =~ a little over one minute. The sensor finder program calculates the allowability of intermittent use when the user fills out the choice for duty cycle.

05/18/17

These sensors have a gold-coated reflecting cone, which can be easily scratched. If one of these sensors needs to be cleaned, we recommend blowing with clean air or nitrogen. If, however, the cone gets soiled (for example with something spilled on it), such that blowing is not enough to clean it, then there is a risk of the contaminant material getting “burned in” by laser radiation. In such a case, to avoid that risk, one should use a suitably soft tissue with solvent, and wipe as gently as possible.

06/23/14

There are a number of options, depending on the purpose.

  • In many cases, the simplest solution could be to make use of the analog output of the meter – that gives a voltage signal proportional to the actual reading (it is in fact just a D/A translation of what is being displayed), so it represents a fully calibrated reading. The full scale value is a function of the meter being used and the power range it is on.
  • The "SH to BNC connector" (Ophir P/N 7Z11010) simply takes the raw output from the detector element and sends it to the scope. It bypasses the sensor's EEROM which contains the calibration data, so it essentially turns the sensor into an uncalibrated "dumb" analog sensor. It should be noted, though, that in some cases we could be talking about a signal to the scope that may be low, perhaps even near the noise level of the scope, which limits the usefulness of this method at low powers.
  • If the need is to see the pulse width – the temporal profile – the solution (assuming applicable specs) is to use an approprinte temporal sensor connected to a scope; you can point it anywhere where it will catch some backscatter from your laser, and you'll see the pulse temporal form as it really is.
05/26/15

Assuming the water temperature and flow rate are stable, the 2 possible concerns in such a case would be:

  • Water condensation on the absorbing surface
     
  • Offset caused by the difference between the ambient room temperature and the temperature of the sensor. The sensor "sees" 2 different temperatures – that of the cooling water flowing inside it, and that of the room air around it. If that temperature difference is small (as it usually is if the water temperature is in the usual specified range), then the air temperature's effect on the sensor body will be negligible compared with the cooling water temperature. However, if it is a large difference, there will be some level of heat flow between the (cold) sensor and the (warmer) air, and this will result in some level of offset in the reading.

 

You can find a lot more information about the correct use of water-cooled sensors in the article "How to use water cooled Ophir sensors", here.

01/15/15

It is fully compatible with these meters/interfaces:

  • Vega / Nova II (firmware vs. 2.44 or higher)
  • Juno (1.31 or higher)
  • StarLite (1.26 or higher)

It is partially compatible with Ophir’s other meters (Nova, LaserStar, USBI, Pulsar, and Quasar). It will function properly with these devices, except with an upper power limit of ~1 mW instead of 100 mW and with reduced accuracy, see specs for more details.

05/26/15

The required flow rate is proportional to the power, i.e. (min flow rate) = (published flow rate at max power)*(actual power input)/(rated maximum power) with the provision that the minimum flow rate should not be less than 1/4 of the published rate at full power.

 

You can find a lot more information about the correct use of water-cooled sensors in the article "How to use water cooled Ophir sensors", here.

01/15/15

Yes, but keep in mind that the RM9 will measure average power, not energy. Also, pulse rates below ~50 Hz may generate additional noise. Pulse rates close to 18 Hz may cause beat frequency issues.

05/26/15

Yes. The BB type thermal sensors will give the correct measurement as long as the wavelength selection is set to the wavelength of the light illumination source.

The measurement for broadband light will be the sum total of the radiation at all wavelengths above and below the wavelength set. However, the accuracy of the reading will depend on how much variation there is in absorption over the entire spectrum. The BB coating is quite flat spectrally (see graph below). In the spectral range of 500nm-1200nm, typical for IPL, the variation in absorption is only about 1.5. So, the accuracy of measuring the total energy will be good as long as you set the wavelength setting to the VIS or <800 selection (which is calibrated at 532nm).


Can I use a thermal BB (broadband) type sensor to measure an IPL source?

03/06/16

Many factors affect the risk of corrosion forming, but the two most important are:

  • the mixture of ions in the water
  • the water’s pH

Our current recommendation is to use DI water – but of a neutral pH. DI water is usually slightly acidic; it can be titrated to a neutral pH, using a bit of sodium hydroxide for example. There are also commercial additives that can help prevent corrosion, for instance Optishield Plus. For a more detailed discussion, see the FAQ at https://www.ophiropt.com/laser--measurement/knowledge-center/faq/7805

 

You can find a lot more information about the correct use of water-cooled sensors in the article "How to use water cooled Ophir sensors", here.

01/15/15

If your source happens to be pulsed at 18 Hz, you cannot use the chopper, since this will generate very low frequency beat signals. However, it might be possible to use the RM9 directly with your laser source, as long as you can connect a BNC sync to the RM9 sensor. Contact us about your particular application to be sure this is the right solution for you.

05/02/16

Corrosion is caused by interactions between the metallic components of the sensor and the cooling water, which may contain a variety of dissolved ions. Many factors affect the risk of corrosion forming, but the most important are the pH and the mixture of ions in the water. For this reason, we recommend using neutral deionized water in a closed circulating system (pH between 6 and 8). Please note that deionized water is usually slightly acidic (pH 5.65) due to absorption of CO2 from the atmosphere. The cooling water can be neutralized by adding 5 ml of a 10 mM solution of NaOH for each liter of water in the cooling system. Commercial additives such as Optishield Plus are also recommended for systems such as ours that have copper and aluminum in them. Optishield has the additional benefit of having biocide to prevent buildup of organic contamination.

To prevent corrosion it is also crucial to not allow standing water to evaporate inside the sensor when it is not in use. When disconnecting a sensor from the cooling system, the water channel should be cleared by blowing compressed air through it.

For those customers still experiencing problems with corrosion, we recommend the new thermal sensor 1000WP-BB-34 which has a special design in which all materials that come into contact with the cooling water are either copper or nonmetallic.

You can find a lot more information about the correct use of water-cooled sensors in the article "How to use water cooled Ophir sensors", here.

06/09/16

This sensor must have water flowing, since the way it works is by measuring (a) the temperature difference between inflowing and outflowing water, and (b) the water flow rate. In other words, the water is part of the measurement mechanism. This is unlike regular water-cooled thermopile sensors, which use water only for cooling – and hence can get away without it in some cases if thermal conditions permit.

05/26/15

Water cooled sensors will not work properly at all unless the sensor is filled with water to make thermal contact between the disc and sensor. If the sensor is filled with water and the input and output connectors are stopped up, then the sensor can be used for a short time without water flow or at much reduced power continuously. Note, however, that when used this way, the response time of the sensor may not be optimal and it may be slow or overshoot.

 

You can find a lot more information about the correct use of water-cooled sensors in the article "How to use water cooled Ophir sensors", here.

11/07/16

Basic use with Profinet requires one power supply cable and one Profinet cable. Using RS232 or the PC application requires one power supply cable and one RS232 cable. If you want to use the Helios in a line/star topology, where it is daisy-chained with the next device in line, then you should use two power supply cables and two Profinet cables.
RS232 uses a standard DB9 RS232 cable. Profinet uses a Profinet-grade cable and RJ45 connectors. The power supply is a standard Profinet power supply from the Han PushPull series. For more information and mating connectors, see Chapter 3 of the manual.

05/26/15

It is not necessary to cool it with water all the time. However, when the water is turned on, there is a transient period where the reading is not stable until the sensor adjusts to the water flow. Therefore, turn on the water before applying the laser and wait until you get a stable reading close to zero before applying the laser. This can take up to 1 minute.

 

You can find a lot more information about the correct use of water-cooled sensors in the article "How to use water cooled Ophir sensors", here.

11/07/16

This is limited by the temperature the Helios body reaches, that is measured by an internal sensor. The temperature shouldn’t be allowed to exceed 60° C. In our experience, this translates to about 40 kJ of accumulated exposure. Of course, the longer one waits in between pulses (allowing the body to cool), the more total energy it can take. That is why the temperature sensor should be used as the primary indicator of overheating, while 40 kJ should be treated as a rule of thumb.

05/26/15

The thermal sensor works by measuring the heat flowing through its sensor. When measuring a short pulse, the heat is absorbed in the sensor absorber and then flows out through the sensing elements. The integral of this heat flow is a measure of the energy. Thus the sensor is actually measuring the energy that flows after the pulse is finished and the pulse width does not matter for this measurement.

11/07/16

There are seven LEDs for different status/error indications. From left to right (and top to bottom), the LEDs are:

  1. Power
  2. COM (Green)
  3. COM (Red)
  4. Link (Port 1)
  5. TX/RX (Port 1)
  6. Link (Port 2)
  7. TX/RX (Port 2)

For more detailed information, see Chapter 7 of the manual.