【正文】 acy. These systems are used in hospitals to test various blood biochemical parameters. All primary health centres, munity health centres, and district hospitals are the potential users of this machine. 2. MATERIALS AND METHODS . The instrument (i) Design principle The instrument is designed using the principle of absorbance transmittance photometry. According to Lambert and Beer’ Figure 1: Schematic of Lambert and Beer’s law. Figure 2: Relation between percent transmission and concentration. law [3], when monochromatic light is passed through coloured solution, the intensity of the transmitted light decreases exponentially with the increase in concentration of the absorbing substance. The value of absorption of light energy is dependent on the number of molecules present in absorbing material and the thickness of the medium. Thus,intensity of light energy leaving the absorbing substance is used as an indication of concentration of that particular shown in Figures 1 and 2, if I0 is the intensity of incident light in coloured solution and It is the transmitted light, then according to this law It = I0e kct (1) and transmission T = It/ I0 = e kct (2) log e T= kct (3) log e(1/ T) = kct (4) 13 where c is the concentration of absorbing material, t thickness of the light path, and k absorption constant. The quantity (logT) or log(1/T) is termed as extinction E/OD or the absorbance: A=log(1/T)=log100/(%transmission) (5) A = 2 log(%transmission). Therefore A = kct. If t is constant, then Aα C. In this system, the basic requirement is to measure optical density/absorbance and then concentration of the test parameter under run accurately. (ii)Microcontrollerbased hardware Figure 3 represents the basic modules of the system。C by initial rates using fixed time, end point, and kiic methods. System allows selecting any required temperature and maintains the temperature of flow cell at that selected temperature because enzymes are relatively fragile substances which have a tendency to undergo inactivation or denaturation [1]. So to get the proper enzymatic rate and for increasing the stability they must be properly handled while conducting the test and must be kept at required temperatures. Temperature sensor LM355 14 Figure 3: Block diagram of clinical chemistry analyser. Figure 4: Microcontrollerbased hardware design of clinical chemistry analyser. and peltier device are used to provide and maintain the required temperature for the samples in flow cell. Peltier works in both directions for cooling and heating. This effect is used to control the temperature of the sample. (iv) Peristaltic pump/aspiration system Port1 of 8031 microcontroller is interfaced with a stepper motor through a driver hardware that drives the roller type of peristaltic pump which generates the required sequence of pulses for the 15 motor driving hardware. The driver hardware enhances the level of voltage for pulse sequences required for the stepper motor. Roller type peristaltic pump used in the system is aspirating the required volume of reagents/samples and for washing the flow cell. This pump can be calibrated to aspirate the required quantity of water, reagent, and samples. (v) Optical module and filter wheel assembly Optical module consists of a light source with reflector, condenser system, collimating objectives, flow cell, filter wheel assembly, and photodiode. Halogen lamp is used as a light Figure 5: Isometric view of filter wheel assembly and Peltier device. source. A constant current power supply is used to power the lamp to reduce the fluctuations in the light. All optical ponents have been designed with quartz glass to have good transmission in UV region at 340 nm. Keeping in view the low response of photo detector in UV (340 nm), all the optical ponents have been provided with enhanced antireflection coating in the UV region. In the optomechanical assembly, special care has been taken in the design so that each ponent is properly aligned with respect to optical axis. To get the required wavelength of light to be passed, 6 interference filters of different wavelengths such as 340 nm, 405 nm, 505 nm, 546 nm, 578 nm, and 630 nm, from UV region to visible region spectrum (300nm to 700 nm), have been mounted on the filter wheel. These filters are selected automatically depending on the test performed. When the filter of required wavel