General Notes on our Products

When specifying our products we use terms such as the quantity Hx, H*(10) or Hp(10) an instrument is designed for, and that an instrument may be PTB approved or PTB certified. We would like to shortly explain these and related terms as far as they concern our products. As to physical background, you can find more information on Radiation Quantities and Units in the »Miscellaneous« category.

Traditional Quantities and Units

The oldest quantity is Exposure Dose measured in R (Roentgen). Its definition is based upon the ability of photon radiation to produce electric charge in air (»ionising« radiation). Instruments measuring Exposure in R have been very popular for many decades and are still in operation.

Another quite old quantity is Absorbed Dose measured in rad (Radiation Absorbed Dose). Absorbed Dose is more a scientific quantity than a quantity related to radiation protection.

Another quite old quantity is RBE Dose measured in rem (Relative Biological Effectiveness Dose). It accounts for the fact that different radiation types (e.g. photons, alphas, neutrons) have different biological effects on human tissue. It is therefore a quantity dedicated to radiation protection of persons. In case of photons it can be assumed that RBE Dose is equal to Exposure Dose, i.e. 1 rem = 1 R. Instruments indicating R could, without any other modification, replace »R« with »rem« now indicating RBE Dose caused by photons.

RBE Dose, introduced in the 1950s, is the first »dose equivalent«. The word »equivalent« is a short form for the »equally hazardous effect« of different types of radiation. In radiation protection we need dose equivalents because, in the end, we want to know how much biological damage radiation produces, not how much ions it produces or how much energy it deposits.

Photon Dose Equivalent Hx

Photon dose equivalent Hx is a quantity introduced in Germany in 1980. Between 1986 and 2001 it was the only legal quantity in Germany. Hx is measured in Sv and defined as

Hx [Sv] = 0.01 Sv/R x Exposure [R].

Since this conversion does not depend on photon energy, Hx is nothing but the good old Exposure Dose in a modern Sv wrapping. Hx was not accepted internationally. Nevertheless we have to mention Hx because it necessarily affected the design of our instruments.

The confusing point is that both the particular German Hx and the international dose equivalents such as H*(10) and Hp(10) use Sv as the unit. Users not familiar with Hx (i.e. almost all users except Germans) may conclude that instruments indicating Sv are designed for the modern dose equivalents. This is not true for Hx instruments. Hx instruments measure Exposure (silently in R), divide the R value by 100, and indicate the result as Sv. Hx instruments may even provide both R and Sv as the unit. For example, our smart Hx models 6150AD5 and 6150AD6 allow the user to select either R or Sv as the unit.

»New« Dose Equivalents

In the meantime the »new« Dose Equivalents are not so new any more. The foundation, however frequently modified thereafter, was the ICRU report 39 from the year 1985. Some countries adopted these new quantities quite early, others later, and some others may still hesitate. According to our knowledge, the USA are a prominent example for a country preferring the traditional quantities for practical radiation protection even today (2015).

A common feature of the new Dose Equivalents is that they are defined in or on a phantom simulating the effect of the human body on the radiation field. Our product range comprises area monitors for the Ambient Dose Equivalent H*(10) and personal monitors for the (Deep) Personal Dose Equivalent Hp(10).

Nevertheless many of our instruments are still available for the traditional quantities. Please see the instruments' individual specifications to learn which quantity they are designed for. If an instrument is available for both traditional and new quantities, both versions are distinguished by model name. Typically models for the new quantities have an extension such as »/H« to the classical type name (e.g. 6150AD6 and 6150AD6/H). Please observe this carefully when ordering.

How differ traditional and new models in design? Their energy response must be different because models for the new Dose Equivalents have to simulate the effect of the phantom. Changing one model into the other requires replacing the energy compensated detector (and minor changes such as replacing the type label). Software or even display elements may also require a change because instruments for the new Dose Equivalents must not use a unit other than Sv.

What means »PTB approved« and »PTB certified«?

According to German (and also European) regulations, instruments measuring relevant quantities have to be officially gauged. Relevant quantities to be measured may be everyday items such as, for example, weight or volume (of goods to be sold at a price based on their weight or volume). In Europe, instruments designed for measuring such quantities are covered by the Measuring Instruments Directive MID. However, particular items such as radiation meters do not fall under the MID, but are subject to national regulations, just like they have always been. For whichever reason Europe could not agree on common rules for radiation meters. In other words, approvals, certificates and similar will not be valid within the entire European Union, but only in the country where they have been issued.

Anyhow, European or national, instruments need some type of official examination if they shall be suited for legal measurements. In Germany, PTB (Physikalisch-Technische Bundesanstalt, as the German national bureau of standards is responsible for such examinations.

Until 2014 the following rules applied: Radiation meters could only be gauged by State Calibration Offices, and only if the meter had a PTB type approval. In order to get the type approval, one had to submit some instrument samples to PTB and they did all the type testing according to their requirements. Once approved, the instruments could be submitted to the State Calibration Offices (not to PTB) to be gauged officially. Note that this gauging does not include some adjustment of the instrument, but is a pure check. If the instrument is within tolerance, it gets a seal at a place to be provided for that purpose. If it is not within tolerance, it is refused.

With the beginning of 2015 various German regulations changed. »Conformity« is now the magic word. The »type approval« system was replaced by »conformity assessment«. Technical procedures did not change, but their names did, and bureaucracy increased. What used to be a »type approval« is now a »type examination certificate«. There is a transitional period of ten years, i.e. until the end of 2024, where type approvals are recognized as type examination certificates. Because they are different names for basically the same thing, we may use both »PTB approved« and »PTB certified« as equivalent terms. Both terms mean that an instrument has been examined by PTB and has met PTB requirements.

The type approval refers to all features of the instrument including its labels and its operating manual. Any deviation from these features is regarded as a violation of the approval. Since equipping the instrument with English rather than German labels is already a deviation, we are not allowed to indicate the type approval on the English version. Whenever we claim that one of our instruments is PTB approved, this shall mean that there is a German PTB approved version of the same instrument. The international (English) version only differs in labels, operating manual, and possibly in some minor software changes we feel appropriate for the international market. Instrument hardware, the most important feature for the instrument's quality, is the same as for the German approved version. Should you insist in having a »really« approved instrument, you would have to accept the German version.

What is the Significance of Automess Calibration Certificates?

We calibrate all of our instruments in the same careful way, no matter whether they are for domestic or foreign customers, and no matter whether they will later be officially gauged or not. Consequently, an officially gauged instrument is not a particularly accurate one, but an instrument whose measuring accuracy has been checked and certified by an independent official body.

We document the result of our calibration in a Calibration Certificate which is included in the delivery. Sometimes we are asked about the character of our Calibration Certificates, particularly whether they are official ones which can be handed to third parties such as authorities as a proof for measuring accuracy. The following information shall answer this question.

We possess an irradiation facility for calibration and radiological check of our instruments. The sources are placed in a lead-shielded container and are activated pneumatically from a remote control room. TV cameras in the irradiation room allow observing the instruments from the control room during irradiation. The irradiation facility is of the same type as used by many German State Calibration Offices. It contains three Cs-137 sources allowing dose rates ranging from a few µSv/h to almost 10 Sv/h. One Co-60 source and an X-ray tube allow to check instrument response at photon energies other than the 662 keV of Cs-137. According to our ISO 9001 certified quality management system we check accuracy once per year with a high precision ion chamber. Additional safety test are performed by German authorities.

This type of equipment is surely very professional. However, we are not an official laboratory with a standard traceable to our national standard at PTB. Therefore, our Calibration Certificates are not official ones (and do not claim to be), they just contain our results obtained with our facility. Nevertheless, we have a permanent comparison with our State Calibration Offices, who in their turn possess standards traceable to PTB. When comparing our Calibration Certificates with the results of these offices, we find differences hardly exceeding 2%, which can be regarded as excellent agreement. This makes us confident that our facility is very accurate.

Recommendations for Periodical Checks

As with any other instrument, it is generally wise or even legally required to check radiation meters at regular intervals. Such a check procedure is often called »calibration«. In order to avoid misunderstandings, we would first like to define the terms »calibration« and »calibration check«:

  • Calibration: calibration means to modify the response of an instrument such that its indication best fits the true value. A calibration of our instruments always requires to open the instrument. This avoids that response could be changed unintentionally. As already mentioned earlier, all of our instruments are calibrated before leaving the factory.

  • Calibration check: calibration check means just to check or verify the response of an instrument without modifying its response. Our Calibration Certificates are examples for such calibration checks which we carry out after we calibrated and closed the instruments.

Why do we emphasise the difference between calibration and calibration check? Because it was common practice, and may still be, to calibrate instruments generally rather than first checking calibration. This practice may have been justified in those days where instruments had analog electronics that were subject to drift. In those days it may have been reasonable to adjust some variable resistors or similar at regular intervals. The purely digital design of modern instruments does not call for such actions because calibration parameters are usually stored in a digital form which cannot drift.

We strongly advise not to calibrate our instruments just on a regular basis, i.e. without the proven need to do so. Calibration is quite an important procedure which, if not carried out carefully enough, may make the instrument poorer than it was before calibration.

We recommend to perform a calibration check first. Unless that check reveals inadmissible deviations (more than ±20%), do not modify the instrument. If there should be significant deviations, first carefully verify that the check procedure was correct. If the instrument is out of tolerance, it will probably require a repair rather than a re-calibration. For example, GM counters are known to behave quite stable. The most frequent errors of GM counters are either that the tube is completely dead (zero indication) or that it is so unstable that indication is much too high. Both errors require replacing the tube, they cannot be compensated by calibration.

How often to perform a calibration check? This may depend on the regulations in your country. Following German regulations we would propose this:

  • Perform a thorough check at intervals of two years. A »thorough« check is a check covering the entire range, see our Calibration Certificates as examples. Thorough checks usually require high dose rates most users cannot provide. In that case they have to be done by institutions like State Calibration Offices.

  • or

  • Perform a low range check at intervals of six months and a thorough check at intervals of six years. A low range check can be done by the user with a relatively small check source such as our 6706. Source holders for that purpose are available for many of our instruments.

Of course, we are also prepared to thoroughly check your instruments. However, depending on which country you live in, shipping costs may by far exceed costs for the check. Whenever possible we strongly recommend to have your instruments checked locally which will save you time and money.

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