Testing of power flow density meters PO-1 by the element-by-element method

Conclusions

• 1. An analysis of expression (7) for the total error in measuring power flow density with set PO-1 shows that up to 50% of this error is due to power reflections in the UHF channel.

• 2. In addition to the testing of PO-1 sets by comparing them with a reference power flow density meter it is also possible to test them successfully by the element-by-element method which consists of the following: a) each UHF element of a PO-1 set is certified (measuring antennas, thermistor heads, attenuators, and bridge M4-2, and the reflection factors of antennas, attenuators, and thermistor heads are tested) at several frequencies in each subrange. b) Factor A² which characterizes for a given instrument the maximum error of this method is calculated from (8). c) If A²≤0.022, and the reflection factors in the UHF channel meet condition (10) or (12), it can be fully guaranteed that the PO-1 set which has been prepared for operation will measure with an error not exceeding±30%.

• 3. A comparison of the component-by-component testing of the PO-1 sets with their testing by means of the method of the VNIIFTRI (All-Union Scientific-Research Institute of Physicotechnical and Radiotechnical Measurements) has shown the correctness of the former method.

• 4. The most unreliable units of the above sets consist of the thermistor heads. Slight overloading of heads leads to changes in their efficiency and the appearance of systematic error L_η, which distorts the measurement results. Therefore, it is advisable to certify thermistor heads as often as possible, for instance, once every quarter and before vital measurements. Unfortunately, the certification of the efficiency of thermistor heads, especially coaxial ones, amounts as yet to a complicated task, because of the small number of testing installations. The production of such installations on the basis of typical and standard components is a very pressing task, because of the large use of thermistor power meters and the more stringent requirements specified for them.