DURRIDGE Company, Services

Service and Repair

Calibration

DURRIDGE maintains a radon calibration facility that includes a controlled, standard source of radon gas. All RAD7 alignment and calibration is done here, as well as basic testing and quality assurance. We determine calibration factors by direct comparison to "master" RAD7's, which were themselves compared with EPA and DOE instruments, and which have participated in international inter-comparisons of radon instrumentation. The calibration accuracy is independently verified by direct determination of the radon chamber level from the calibrated activity and emission of the standard radon source. In addition, we regularly intercompare with other radon chambers. We achieve a reproducibility of better than 2% with our standard RAD7 calibration. Overall calibration accuracy is better than ±5%.

The EPA recommends, and we agree, that continuous radon monitors be calibrated at least every year. RAD7 calibration requires four to five working days from the receipt of the instrument. And we usually return it to you via the same shipping method you used to get it to us - from "slow boat" to "next day air". As a preliminary to recalibration, we inspect and test every RAD7. If additional service is required, this may delay the return of the instrument.

We recommend that you arrange for your calibration ahead of time, to avoid possible delays. When sending your RAD7 for calibration, please send the instrument only, without the accessories, and please pack it well, with at least an inch of packing all round.

Thoron Calibration

The RAD7 is able to measure both radon (222-Rn) and thoron (220-Rn) concentrations simultaneously and independently. The standard radon calibration is performed with a precision of better than 1% and we guarantee the RAD7 absolute accuracy for radon to be better than 5%. However thoron has a very short half life (about one minute) so that the concentration in the air will change during sample acquisition. For every minute the sample gas is in transit from the sampling point to the measurement chamber, the concentration of thoron in the sample will drop by half.

The RAD7 manual describes the standard setup for thoron sniffing. It is designed to minimize the transition time of the air sample from sampling point to measurement chamber. The pump runs continuously and the desiccant is in a small tube. In those conditions, the acquisition time is about one minute, so the default thoron sensitivity of the RAD7 is set at half the radon sensitivity. This setting is sufficient for most applications.

For example, when trying to locate radon entry points, it is sufficient to find locations where there is measurable thoron to know that there is a fresh soil gas entry point nearby. Anywhere else in the building, far from a radon entry point, the thoron will have decayed away to practically nothing, so just finding thoron and zeroing in on the highest reading achieves the object of locating the radon entry point. For this application, it is necessary to use the RAD7 in thoron protocol, and it is necessary for the thoron readings to be repeatable and in correct relation to each other. The standard (thoron protocol) RAD7 setup, with the default thoron sensitivity setting, provides all the functionality and accuracy necessary for this application.

Occasionally a user requires more accurate thoron readings. For these applications DURRIDGE Company can provide, as an option, a specific thoron calibration for the setup used by the user. The detailed conditions of the calibration, including the air flow rate, may be chosen by the user and are clearly specified in the thoron calibration certificate issued by DURRIDGE. For any other setup, with a different flow rate or a different volume in the sample air path, that thoron calibration is no longer valid. For some projects, DURRIDGE Company has provided multiple thoron calibrations, each for a different setup of the RAD7 and air sample acquisition path.

Please note that while the thoron sensitivity of the RAD7 is strongly dependent on the sample air transit time, from sampling point to measurement chamber, the radon sensitivity of the instrument is constant (to within 1%) and independent of the sample air transit time provided this is less than one hour. The standard radon measurement (not thoron protocol) will refresh the air in the measurement chamber once every five minutes, so that the radon level is kept up to date.

Repair

If you discover that your RAD7 is malfunctioning, we recommend that you first call DURRIDGE and talk to a technician. A surprising number of minor "disasters" can be avoided by long-distance consultation. The next step, if consultation fails, usually is to send your instrument in for evaluation and repair. Please send any documentation of the problem that you might have (notes, printouts, etc.) and a short note describing the problem. Be sure that you put your name and telephone number on the note. Within 48 hours of our receipt of the instrument, we will call you to give a diagnosis.

Bear in mind that a repaired instrument often requires complete re-calibration, so a one-week turn-around may be the best we can do. If you absolutely need an instrument during the repair time we can sometimes arrange to send you a "loaner" instrument.

Shipping

The RAD7 is shipped to you in a plastic bag, packed in a box with "popcorn", and finally packed inside another box that also holds all the accessories. The inner box, by itself, is too small for the return trip, when you need a calibration or repair job. You need to find a bigger box, with space for one inch packing all round the RAD7. A 14" cube box is fine. Pack and seal the box carefully.

Please do not ship any accessories, unless they are relevant to the problem.

All return shipments to DURRIDGE must be prepaid, and unless you instruct us otherwise, we'll return it to you via the same shipping method you used to get it to us - from "slow boat" to "next day air", freight collect.

Upgrades

Whenever you send your RAD7 in for repair or calibration, you have the option of having the latest available software installed. Most RAD7's can be upgraded to the latest hardware configuration as well. You will be informed periodically of whatever new features are available for your RAD7. Please advise if you want to have an upgrade made. We intend to keep our RAD7 customers happy by keeping their instruments up-to-date, state-of-the-art.