The use of computers for for modelling fermentation processes started in 1960s. Initially the use of computers was restricted because of the cost factor but reductions in the cost and the availability of the cheaper small computers has widened interest in their possible applications. The availability of efficient small computers has led their use for pilot plants and laboratory systems because the financial costs for the online computer systems counts the insignificant part of the whole system. There are three distinct systems areas of computer function postulated by Nyiri in 1972:
a) Logging of Process Data: This is performed by the data acquisition which has both hardware and software components. there is an interface between the sensors and the computer. the software should include the computer program for sequential; scanning of the sensor signals and the procedure of data storage.
b) Data Analysis: Data reduction is performed by the data analysis systems which is acomputer program based on a series of mathematical equations. the analysed information may be put on a print out, fed into data bank or utilized for process control.
c) process control: is also performed by a computer program. signals from the computer are fed tio the pumps, valves or switches via the interface. in addition to this computer program may contain instructions to display devices or teletypes to indicate alrms.
Components of Computer Linked system:
When a computer is linked to a fermenter to operate as a control and recording system, a number of factors must be considered to ensure taht all the components interact and function satisfactorily for the control a d data logging.An example is DDC (Direct Digital Control) system to explain the computer controlled addition of a liquid from a resrvoir to a fermenter.
A simple outline of the main components is as follows:
Sensor S in fermenter produces a signal which may need to be simplified and conditioned in the correct analogue form. at this stage it is necessary to convert the signal to a digital form which can be subsequently transmitte dto the computer. An interface is placed in the circuit at this point. The interface serves as the junction point for the inputs from the fermenter sensors to the computers and output signals from the computer to the fermenter controls such as a pump T attached to an additive reservoir.
A sensor will generate a small voltage proportional to the parameter it is going to measure. for example a temperature probe might generate 1V at 10oC and 5V at 50oC. But this signal cannot be understood by the computer and must be converted from an analogue to digital converter ( ADC) into digital form.
The accuracy will depend upon the number of bits it sends to the computer. AN 8-bit converter will work in the range of 0-255 and it is tehrefore able to divide a signal voltage into 256 steps. This will give amaximum accuracy of 100/256, which is pproximately 0.4%. However a 10- bit converter can give 1024 steps with a n accuracy of 100/1024, which is pproximately 0.1%. therefore when a parameter is to be monitored very accurately a converter of the appropraite degree of accuracy will be required. the time taken for an ADC to convert voltage signals to a digital output will vary with accuracy, but improved accuracy will lead to slower conversion and hence slower control responses. The small computers is often used for one or more fermenters. it is coupled to a real time clock, which determines how frequently readings from teh sensor should be taken and possibly recorded. Ancillary equipments include a VDU, a data store , a teletype, a graphic display unit, a print out, alarms and barometer.
It is also possible to develop online programs so that online instruments can be checked regularly and recalibrated when necessary.