V.V. Oreshko - Head of Group of Research Engeneer, JSC «Russian space systems» (Moscow). E-mail: viktororeshko@mail.ru A.I. Kulikov - Head of Sector, JSC «Russian space systems» (Moscow). E-mail: tm016@rniikp.ru P.E. Romanov - Leading Engeneer, JSC «Russian space systems» (Moscow). E-mail: tm016@rniikp.ru

The additive error arising at measurement of analogue slowly changing parametres by onboard radio telemetry systems is considered. In article the simplified plan of measuring of analogue slowly changing parametres is given. Sensing transducers have on an exit voltage from 0 V to 6,25 V. In the course of measurement at first there is a capacity charge on an entry of the buffer cascade to level 9 V. Then there is a sensing transducer switching on an entry of the buffer cascade. The capacity of the buffer cascade is discharged through an output resistance of the sensing transducer and capacity of a cable network to level of voltage of the sensing transducer. Then there is an analog-digital conversion. ADC it is used eight-digit, that is only 256 levels of quantization. The buffer is calculated so that the lower value of a scale (0 V) - 5 level of quantization, the upper value of a scale (6,25 V) - 250 level of quantization. If more than 250 level of quantization - the communication line with the sensing transducer is broken. The capacity of the buffer cascade is not discharged to level of voltage of the sensing transducer, so we have exit for scale limits. That is the indication of broken cable network. The capacity of the buffer cascade is not in time will be discharged to level of voltage of the sensing transducer if the output resistance of the sensing transducer is more 1 kOhm, or the capacity of a cable network is more than 10 nF. Effect of it is the additive error. The considered circuit of measurement of analogue slowly changing parametres settled up proceeding from following requirements: resistance of the sensor no more than 1 kOhm, and frequency of inquiry does not exceed 200 Hz. The increase in frequency of inquiry of sensors conducts to not predicted increase in an additive error. Because analogue-digital conversion will occur during the transient termination in the buffer cascade. In article the formula for evaluation of the additive error is calculated. Graphs of association of an additive error from value of voltage of a sensor, time, capacities of a cable web and resistance of a sensor are presented. The simplified formula for error calculation is given.

 

1. Nazarov A.V., Kozyrev G.I. i dr. Sovremennaja telemetrija v teorii i na praktike. Uchebnyjj kurs. SPb.: Nauka i tekhnika. 2007. 672 s.
2. Bessonov L.A. Teoreticheskie osnovy ehlektrotekhniki. M.: Vysshaja shkola. 1996.
3. KHorovic P., KHill U. Iskusstvo skhemotekhniki. Izd. 5-e. M.: MIR. 1998.
4. Krasovskijj A.A., Pospelov G.S. Osnovy avtomatiki i tekhnicheskojj kibernetiki. M. - L.: Gosehnergoizdat. 1962. 600 s.
5. Tekhnicheskijj spravochnik. Kabeli, provoda, materialy dlja kabelnojj industrii. Nauchno-proizvodstvennoe predprijatie NKP «EHllips». 2006.
6. Vishnjakov E.M., KHvostov D.V. Vlijanie skrutki na mezhprovodnikovuju emkost vitykh par i triad // Kabel-news aprel 2007. №4.