Abstract Details
| Name: Kumar Affiliation: ARIES Conference ID: ASI2016_964 Title : Upgradation of the 104 cm ARIES Sampurnanand telescope Authors and Co-Authors : T. S. Kumar, A.K. Singh, Lalit Dalakoti and Biman Medhi Abstract Type : Poster Abstract Category : Instrumentation and Techniques Abstract : In this paper we present the updradation activities being planned for the electrical system of the 104 cm Sampurnanand telescope at ARIES, Nainital. The telescope has f/13 optical system and is supported on off-axis equatorial mount. For pointing both right accession (R.A.) and declination (Dec) axes are provided with four different three phase ac induction motors running at fixed speeds on a UPS power supply. Suitable gear boxes are used with each motor for providing slew, set, fine I and fine II motions ranging from 2 deg/sec to 1 arcsec/sec. A 15 KVA 3 phase UPS is used for operating the entire telescope system including the dome, the instruments and the interfacing PCs. Tracking is achieved using an additional induction motor driven by an inverter which maintains a fixed frequency for providing a constant speed of 15 arcsec/sec. The inverter has two parts: a three phase signal generator and a power amplifier stage. Sidereal time is generated with the help of a 220 v ac, 50 Hz shaded pole induction motor, hour angle (H.A.) and R.A. syncro transmitters and receivers and a differential gearbox. A user operates the telescope using a push button console and the synchro transmitter and receiver dials display R.A., H.A., Dec and sidereal time. The existing electrical system used for controlling the telescope is more than forty years old and most of the components have become obsolete. The drive electronics originally installed for the sidereal clock and tracking motor are based on analogue electronics with components that are no longer available. Since the telescope employs electrical contractor logic and separate motor for each speed the system is quite robust and simple to maintenance. Hence for the upgradation work we combined the robustness of the electrical system and the advantages of the modern microcontroller based systems. The sidereal clock drive has been upgraded with in-house developed microcontroller based single phase digital drive with PWM output. While the tracking drive signal stage has been replaced with a microcontroller based 3 phase signal generator. For RA and Dec slew motions commercially available three phase Siemens drives has been employed and are tuned to provide smooth acceleration and deceleration. Three phase soft starters are used for the set motions and the remaining fine motions are switched directly. A similar contactor logic has been developed for commanding the telescope and for safety interlocking. Here both the RA and Dec functions have been separated in two different electrical panels and can be interfaced with a microcontroller based system. The RA panel has been commissioned successfully while the Dec panel is being developed. Later, the panels will be interfaced with microcontroller system and the telescope would be commanded using a GUI based PC. The drive parameters, the command status, the telescope status and errors could be continuously monitored and logged. A mechanical assembly for coupling the encoders to the main axes is being developed in our workshop. This would help in improving the pointing and tracking accuracies and enable GPS based sidereal time. |