The length of calibration intervals is determined directly by the organization operating the meter on the basis of the company’s metrological regulations.
With regard to the fact that devices for inspections of electrical equipment are not among the so-called
Determined gauges, where the calibration interval is clearly determined, it is good to take into account the following factors when determining the time between two calibrations:

• Manufacturer’s recommendation – a basic and very important piece of information that should be respected.
• Conditions of use – measuring instruments are usually quite complex devices, and although manufacturers strive for their maximum durability, the conditions of use play a very important role in determining the calibration interval.
  It is obvious that the meter that the company sometimes uses to check appliances within its own company will be significantly less stressed than the same device with which its user performs dozens of inspections of appliances on construction sites every day.
• Track the history of calibration certificate data – by comparing the measured values, you can see the trend of the change in the accuracy of your measuring instrument.
  If it is clear from the calibration certificates that the accuracy of none of the measured quantities is constantly deteriorating, you can afford to extend the existing calibration interval.
  Of course, it is necessary to take into account, for example, the repair or adjustment of the measuring instrument, where there may be a step change in the data in the monitored series of data.
• Overloading, repairing or suspected malfunction of the instrument can be a serious reason for shortening the calibration interval.
  If the instrument is repaired directly by the manufacturer or an authorised service centre, you may be notified that calibration of the instrument is recommended.
  It is highly advisable to respect this recommendation, because even if the instrument is adjusted after the repair, according to the Metrology Act, the repair of the meter is given as an example of the need for calibration.

Every company – and it does not matter whether it is a sole trader or a large company – should have a Metrological Code of the company.
Of course, in large companies, corporate metrologists are dedicated to this area, for sole traders and small companies it is recommended to prepare their own Metrological Code of the company, which in its simplest form should contain:

• Unambiguous identification of the company – name, address, ID number, responsible person
• List of measuring instruments subject to calibration – for each instrument there is a type, manufacturer, serial number, calibration interval and individual calibration dates.

Each meter subject to calibration should be labeled with the date of the next calibration by the user, which will reduce the possibility of missing the calibration with regular use of the meter.

The MDtest device is not a medical device within the meaning of Act No.
268/2014 Coll.
on medical devices and in accordance with Act No.
366/2017 Coll.
and it is a working gauge – see the previous question: How often should I calibrate inspection instruments and who determines the calibration interval?

To put it very simply: anyone who has ensured the demonstrable continuity of the gauges used for calibration.

Of course, when setting up a calibration laboratory, all legal and technical requirements stipulated by the Metrology Act and related regulations must be met, but the calibration laboratory does not receive any certificate or other document from the superior authority that it is authorized to calibrate measuring instruments, and it is therefore unnecessary to require these documents.

It is true that you may once receive a calibration certificate with a satisfactory verdict from the same calibration laboratory, and sometimes the calibration certificate contains only the measured data.
The explanation may be as follows: if the calibration certificate comes directly from the manufacturer of the gauge and it is an initial calibration, it is usually written in the calibration protocol that the device complies with the accuracy given by the technical parameters at the time of calibration.
In other cases, the statement is usually not given for the following reasons, for example:

• The calibration laboratory does not know the basic error or even the general technical conditions of the calibrated gauge and therefore cannot determine whether the accuracy of the gauge complies or does not comply with the technical conditions according to the manufacturer.
• Some of the ranges or some quantities do not meet the technical requirements according to the manufacturer – but this does not mean that the device must not be used.
  An example of an insulation meter can be given, where another function is voltage measurement.
  In many cases, the voltage measurement does not meet the accuracy stated by the manufacturer, but the measurement of insulation resistance is perfectly fine.
  If the meter is clearly and distinctly marked with a label that draws attention to the fact, nothing prevents its use.
• A measurement error in any of the ranges does not meet the manufacturer’s technical requirements – for example, instead of the manufacturer’s stated 2%, the measurement error will be 4%.
  However, if the user is able to prove that the mentioned measurement error of 4% is also satisfactory for his measurements, the device can be used without any problems.

Although manufacturers or retailers often refer to this device as a “calibration fixture”, its use is in no way a substitute for gauge calibration.
This product can only be used to check some functions of the device in case of doubt, the product itself does not have the necessary metrological qualities or metrological traceability.

Although calibration only applies to the measuring instrument, it is advisable to hand over the measuring leads, or tips and crocodile clips with the instrument – the calibration laboratory should use these accessories when calibrating the gauge and thus possibly detect, for example, increased contact resistance in the connectors.
The calibrated device must also be accompanied by:

• An order with the exact address of the customer, the agreed method of delivery and payment, and if complete calibration of the meter is not required – then also by defining the scope of calibration – i.e.
  with specification of quantities and ranges
• Instructions for use of the device (a copy is sufficient).
  Although all calibration laboratories have a collection of manuals for the most common types, individual devices may differ in firmware, technical parameters and control methods.
• Reliable contact to the customer – preferably a mobile phone number and an e-mail address.
• Description of any problems that occurred between two calibrations (instability of the reading, excessive fluctuations, problems with measurement repeatability…)

Most calibration laboratories do not require an old calibration certificate.

Here are some tips that may help:

• Arrange a specific date for handing over the meter to the laboratory.
• Calibration laboratories usually have longer deadlines during holidays and before the end of the calendar year.
• Most calibration laboratories offer an express service, where a shortened date is guaranteed for an additional fee.
• Avoid calibration laboratories that are willing to write a calibration sheet without measuring.
  You would save time and sometimes money, but it is a reliable way to get into trouble.
• You can find information about the workload of our calibration laboratory in the Calibration of Instruments section

Although calibration prices do not differ drastically from calibration laboratory to calibration and the ways of possible savings are therefore relatively limited, there are other safe ways to reduce calibration costs:

• Use the calibration certificate data to monitor the stability of your instruments.
  If the instruments do not tend to use the full permissible errors, you can extend the calibration interval recommended by the manufacturer, for example, by six months.
• Have only those quantities and ranges calibrated that you use during work.
  The cost of calibrating a conventional handheld multimeter will be significantly reduced if temperature and capacitance measurements, for example, are not calibrated and the range of voltage and current calibrations is limited.
• Some measuring instruments were often labeled “Informative meter” by users to indicate that this meter is not subject to calibration because it is only used for indicative measurements – a typical example is a voltmeter, which is only used to determine whether there is a phase or combined voltage between the wires, and I don’t care whether I measure 229 V or 232 V. Because current metrology does not know the term “Informative meter”, It is possible to set a calibration interval longer than the expected lifetime of the gauge – for example 10 years.
• Take care of your instruments – a simple calibration can turn into a repair due to the fact that the devices are stored in inappropriate areas, are knocked without transport packaging in car trunks, are operated without respecting the instructions in the operating instructions.