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Tickoo, A. K.; Koul, R.; Kaul, S. K.; Kaul, I. K.; Bhat, C. L.; Bhatt, N.; Kothari, M.; Goyal, H. C.; Agarwal, Nikita; Kaul, S. R.

doi:10.1023/a:1008090931239

Cited by 9 publications

(5 citation statements)

References 2 publications

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“…Eight such encoders are being presently used in the fourelement TACTIC (TeV atmospheric Cherenkov telescope with imaging camera) array of atmospheric Cherenkov telescopes [21]. Each telescope of the array uses two encoders for monitoring its zenith and azimuth angle so that the drive control software [22] can be operated in a closed-loop configuration for tracking a celestial source. The calibration of the encoders was carried out with a rotary table of a coordinate measuring machine (make: Zeiss, Germany; model: RT 05-300).…”

Section: Measurement Of Encoder Error Profilesmentioning

confidence: 99%

Artificial neural network-based error compensation procedure for low-cost encoders

Dhar¹,

Tickoo²,

Kaul³

et al. 2009

Meas. Sci. Technol.

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: An Artificial Neural Network-based error compensation method is proposed for improving the accuracy of resolver-based 16-bit encoders by compensating for their respective systematic error profiles. The error compensation procedure, for a particular encoder, involves obtaining its error profile by calibrating it on a precision rotary table, training the neural network by using a part of this data and then determining the corrected encoder angle by subtracting the ANNpredicted error from the measured value of the encoder angle. Since it is not guaranteed that all the resolvers will have exactly similar error profiles because of the inherent differences in their construction on a micro scale, the ANN has been trained on one error profile at a time and the corresponding weight file is then used only for compensating the systematic error of this particular encoder. The systematic nature of the error profile for each of the encoders has also been validated by repeated calibration of the encoders over a period of time and it was found that the error profiles of a particular encoder recorded at different epochs show near reproducible behaviour. The ANN-based error compensation procedure has been implemented for 4 encoders by training the ANN with their respective error profiles and the results indicate that the accuracy of encoders can be improved by nearly an order of magnitude from quoted values of ∼± 6 arc-min to ∼±0.65 arc-min when their corresponding ANN-generated weight files are used for determining the corrected encoder angle.

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Section: Measurement Of Encoder Error Profilesmentioning

confidence: 99%

Artificial neural network-based error compensation procedure for low-cost encoders

Dhar¹,

Tickoo²,

Kaul³

et al. 2009

Meas. Sci. Technol.

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“…The new co-ordinates of the source are calculated after every second while tracking a candidate source. More details regarding various hardware components of the telescope drive system are discussed in [19].…”

Section: Drive Control Systemmentioning

confidence: 99%

The TACTIC atmospheric Cherenkov imaging telescope

Koul

Tickoo

Kaul

et al. 2007

Nuclear Instruments and Methods in Physics Research Section A:

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The TACTIC γ-ray telescope, equipped with a light collector of area ∼9.5m 2 and a medium resolution imaging camera of 349-pixels, has been in operation at Mt.Abu, India since 2001. This paper describes the main features of its various subsystems and its overall performance with regard to (a) tracking accuracy of its 2-axes drive system, (b) spot size of the light collector, (c) back-end signal processing electronics and topological trigger generation scheme, (d) data acquisition and control system and (e) relative and absolute gain calibration methodology. Using a trigger field of view of 11×11 pixels (∼ 3.4 • ×3.4 • ), the telescope records a cosmic ray event rate of ∼2.5 Hz at a typical zenith angle of 15 • . Monte Carlo simulation results are also presented in the paper for comparing the expected performance of the telescope with actual observational results. The consistent detection of a steady signal from the Crab Nebula above ∼1.2 TeV energy, at a sensitivity level of ∼5.0σ in ∼25 h, alongwith excellent matching of its energy spectrum with that obtained by other groups, reassures that the performance of the TACTIC telescope is quite stable and reliable. Furthermore, encouraged by the detection of strong γ-ray signals from Mrk 501 (during 1997(during and 2006(during observations) and Mrk 421 (during 2001(during and 2005(during -2006 observations), we believe that there is considerable scope for the TACTIC telescope to monitor similar TeV γ-ray emission activity from other active galactic nuclei on a long term basis.

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“…The γ -ray telescope array Tera-electron-volt Atmospheric Čerenkov Telescope with Imaging Camera (TACTIC) consists of synchronously tracking light collectors of area 4 × 9.5 m 2 which are placed at the centre and the three corners of a triangle of side 20 m. It is at present in the installation phase at Mount Abu (24.6 • N, 72.7 • E, 1400 m above sea level) in the western Indian state of Rajasthan [1]. We restrict our discussion here to the IE of the TACTIC (figure 1(a)) which has already been commissioned.…”

Section: The Tactic Imaging Elementmentioning

confidence: 99%

“…Being invariably exposed to different night-sky background light levels for a variety of reasons, including zenith-angle and sky-transparency variations, the individual pixels normally experience variations in their SCRs and anode currents. These variations are further enhanced by the phenomenon of star-field rotation [1,2], which is inherent to altitude-azimuth mounted telescopes, like the TACTIC. This causes the image of an off-axis bright star in the field of view of the telescope to trace a circular path in the focal plane, possibly with large variations both in the SCR and in the corresponding anode current in the pixels concerned over typical time scales of tens of minutes.…”

Section: The Tactic Imaging Elementmentioning

confidence: 99%

“…Noting that this parameter bears a rather simple power law relationship with the channel HV (and hence anode current) for a given value of the incident light flux (see section 3 below), we were persuaded to monitor the anode current indirectly, through logging of the SCR. This method allowed us to dispense 1 Present address: Inrange Technologies, USA.…”

Section: Introductionmentioning

confidence: 99%

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On a single-counts rate stabilization scheme employed in the imaging camera of the TACTIC γ-ray telescope

Bhatt¹,

Yadav²,

Kanda³

et al. 2001

Meas. Sci. Technol.

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A cost-effective methodology for operating the 349-pixel Cerenkov light imaging camera of the imaging element of the TACTIC γ-ray telescope array at stable single-counts rate and safe anode current values has successfully been tried out despite variations in the light of the night sky experienced by these pixels from time to time. Important details of this unconventional scheme are discussed and reference is made to the methods evolved for in situ absolute and relative gain calibrations of the camera pixels, which are particularly required for this mode of operation.

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Cited by 9 publications

References 2 publications

Artificial neural network-based error compensation procedure for low-cost encoders

Artificial neural network-based error compensation procedure for low-cost encoders

The TACTIC atmospheric Cherenkov imaging telescope

On a single-counts rate stabilization scheme employed in the imaging camera of the TACTIC γ-ray telescope

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