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Abstract
Abstract
NIRS has been successfully applied to determine chemical content of various materials. However, the commercial NIR instrument can not measure many samples in one measurement time so the faster measurement can not be realized. The purpose of this research are (1) to modify NIR instrument designed
by Budiastra et al. (1998) so it can be used to measure absorbance of some samples in one measurement time, and (2) to test the performance of the modified NIR instrument in measuring the absorbance of coffee. The modified NIR instrument consists of optical unit, electronic unit and mechanical unit (auto-sample holder). A new mechanical unit (auto-sample holder) has been developed to measure reflectance of some samples automatically. The performance of modified NIR instrument was evaluated by its consistency, delay time, detect ability for different water content and compared to other NIR instrument. The consistency of instrument is high with the percentage of homogeneity of 98.65%. The optimal delay of measurement is 200 ms. The modified NIR instrument is able to measure the different water content of coffee. The modified NIR instrument have same pattern of absorbance characteristic and higher than other NIR instrument, since the modified NIR instrument used integrating sphere and a large amplifier signal amplification.
Abstrak
NIRS telah berhasil dimanfaatkan untuk menentukan kandungan kimia berbagai macam bahan. Namun, instrumen NIR komersial tidak dapat mengukur banyak sampel dalam satu waktu pengukuran, sehingga pengukuran dengan waktu yang lebih cepat tidak tercapai. Tujuan dari penelitian ini adalah (1) memodifikasi instrumen NIR hasil desain Budiastra et al. (1998) supaya dapat digunakan untuk mengukur beberapa sampel dalam satu waktu pengukuran dan (2) menguji kinerja instrumen NIR hasil modifikasi untuk mengukur absorbansi dari biji kopi. Instrumen NIR hasil modifikasi terdiri dari unit optik, unit elektronik
dan unit mekanis (auto-sample holder). Unit mekanis (auto-sample holder) dibuat untuk mengukur reflektan beberapa sampel secara otomatis. Kinerja instrumen NIR hasil modifikasi dievaluasi berdasarkan konsistensi, waktu delay, kemampuan mendeteksi perbedaan kadar air dan perbandingan dengan alat NIR lain. Konsistensi hasil pengukuran instrumen NIR menunjukkan nilai yang tinggi dengan persentase kehomogenan sebesar 98.65%. Delay optimal pengukuran sebesar 200 ms. Instrumen NIR hasil modifikasi mampu mengukur kadar air biji kopi yang berbeda. Instrumen NIR hasil modifikasi mempunyai pola
karakteristik absorbansi yang sama dan lebih tinggi daripada instrumen NIR lain, dikarenakan instrumen NIR menggunakan integrating sphere dan penguatan sinyal amplifier yang besar.
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