4 Operations/Analysis Unit
direct meter indication, which greatly eases the task of balancing the system during initial system installation and periods of calibration.
The DC voltage levels are fed to a logarithmic ratio amplifier which pro- duces a voltage output that is proportional to the logarithm of the ratio of the two DCinputvoltages.Thisoutputvoltage,directlyproportionaltotheconcentration ofsample,is,withincertainlimits,alinearfunctionoftheconcentration.For purposes of transmission, the voltage signal is converted by an E-to-I converter; thus,theoutputsignalfromtheanalysisunitisacurrentsignalthatisproportional to the concentration of sample in the sample module.
There is also an option of providing an automatic zero function (see draw- ingB-14729)inthecontrolunit.Thiscircuitprovideselectricalsignalsfor switchingafluidwhichcontainsnoneofthematerialtobemeasuredintothe samplemodule,electricallyadjustingthezerosandswitchingbacktosample.
4.4.1Source Module
The source module is the source of infrared energy. This is provided through the use of a high-intensity mini IR lamp or a quartz iodine lamp operating directly from a 5.0 volt stable supply or a 6.3 V transformer. To ensure a stable source of radiation in the face of line-voltage variations, the lamp transformer derives its input directly from a line voltage-regulating transformer, selected for its ability to maintain a constant output voltage level regardless of fluctuations in the input line voltage within the control range of 105 to 130 VAC.
In some applications where we have an abundance of energy due to low sample absorption, the focusing lens is removed to avoid excess energy reaching the detector. However, other systems have high energy losses in the sample module due to strong sample absorbance or exceptionally long sample path-lengths. These systems require a focusing lens to gather and collimate the radiation for maximum utilization of source energy. The collimating lens is usually quartz, but may be CaF2 for longer wavelengths. Also the source lamp may be a differenct type, to emit more radiation at the longer measuring wavelengths. (Consult manual addendum descriptions).
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TeledyneAnalyticalInstruments
A Business Unit of Teledyne Electronic Technologies
