Patent GB-1349156-A (GB)
Title: Automatic calibration apparatus
Inventor: GASIUNAS D V
IPC: G01N21/31
Filed: 1971-11-01
Abstract: 1349156 Selective signalling TECHNICON INSTRUMENTS CORP 1 Nov 1971 [30 Oct 1970] 50720/71 Heading G4H Calibration apparatus for multi-channel sample analysis means, determines and applies to the signal in each channel respective background and calibration factors, an A/D converter being used in the application of the background factors.  Six measurement channels of an atomic spectroscopy analysis apparatus are multiplexed through a switched gain amplifier to a multiplexed integrator having a storage capacitor for each channel. The amplifier comprises an AC amplifier with a gain of x 1 or x 1000 and a D.C. amplifier with nine steps of gain x 2. A digital memory holds a 5-bit level set (gain) word for each channel, to control the gain of the switched gain amplifier, the words being produced as follows. The gain word 10000 is supplied from a sequence counter via an intermediate data storage and decoding unit to switch in the x 1000 gain. The integration results (in the multiplexed integrator, see above) with this gain are compared, channel by channel, with a reference, the gain word being recirculated into the digital memory with the highest order bit at 1 or 0 according to the comparison result for the channel. Subsequent bits of the gain words are built up similarly. The multiplexed integrator and digital memory are addressed, during this, by a channel address counter driven in sync. with a filter wheel in the analysis apparatus. Zero set (background) words for the channels are determined as follows. With a zero concentration standard flowing through the analysis apparatus, the integrated value (in the multiplexed integrator) for the channel in question is used to charge a further integrator, with concurrent incrementing of a BCD up/down counter by standardrate clock pulses from a rate multiplier, until the counter overflows to all zeroes, when a constant negative source is switched in to discharge the further integrator, incrementing of the counter continuing until the integrator reaches zero. The count is transferred in parallel form to another section of the digital memory, as the zero set word. Such a word is obtained for each channel in turn. A calibration word is obtained for each channel as follows. With a standard solution with known concentrations of the constituents measured by the respective channels flowing in the analysis apparatus, and with concentration words specifying the concentrations having been loaded into a further section of the digital memory, the integrated value (in the multiplexed integrator) for the channel in question is used to charge the further integrator (see above), with concurrent incrementing of the up/down counter by the standard-rate clock pulses from the rate multiplier. When the up/ down counter overflows to all zeroes, the constant negative source is switched in to discharge the further integrator, and at the same time, the zero set word for the channel is read from the digital memory and set into the up/down counter (which continues to count up). When the counter reaches all zeroes again, a calibrate word, which is all zeroes apart from the highest order bit which is one, is applied to the rate multiplier to control the rate of the clock pulses still being fed to the up/down counter. When the further integrator reaches zero, the counting is stopped and the count is compared in a digital comparator with the concentration word for this channel from the digital memory, the calibrate word being placed in a further section of the digital memory with its highest order bit set according to the comparison result. The operation repeats to determine the other bits of the calibrate word in turn, by setting successive bits of the word to one, the higher-order bits of the word already determined having their determined values during this. The calibrate words for the other channels are then determined similarly. During use of the system for measuring unknown concentrations using the respective channels, the procedure for each channel is as follows. The switched gain amplifier has its gain controlled by the level set word. The further integrator is charged from the multiplexed integrator, with incrementing of the up/down counter by clock pulses, overflow to all zeroes causing initiation of discharge of the further integrator using the negative source and setting of the zero set word into the counter. When the counter overflows to all zeroes again, the clock pulse rate is set in accordance with the calibrate word. When the further integrator reaches zero, counting is stopped and the count is transferred to a further section of the digital memory for print-out.