3160 - Trace oxygen analyzer - Teledyne Analytical Instruments

Operational Theory 2The analog output printed circuit board (PCB) generates the two 0–1 volt and thetwo 4–20 mA analog signal outputs available on the rear panel of the analyzer. Thesesignals, generated in digital format by the microcomputer, are converted into analogsignals by the circuitry on this PCB. The output signals represent the following:• 0–1V Signal (Oxygen Measurement): This output goes from 0 to 1, representing0 to 100% of the scale that has been set; i.e., 0.6 volt is equal to 60% of the fullscale, or 6 PPM when on the 10 PPM scale. It is possible that the signal may go pastzero into the negative range up to -0.25, especially if the analyzer has been zeroedwith a gas that contains a significant concentration of oxygen. See Figure 2-3.• 0-1V Range Identifier: This 0 to 1 volt output represents each range with aparticular voltage as shown in Table 2–1.• Isolated 4–20 mA Signal (Oxygen Measurement): This is a 4 to 20 mA outputrepresenting 0 to 100% of the scale, with 4 mA equal to 0%, and 20 mA equal to100% of that range. This output may also range lower than 4 mA, especially if theanalyzer has been zeroed with a gas that contains a significant concentration of oxygen.See Figure 2-3.• Isolated 4–20 mA Range Identifier: This 4 to 20 mA output representsindividual ranges with discrete current output as shown in Table 2-1.Table 2-1. Range IdentifierIdentifier IdentifierRange Scale Voltage (V) Current(mA)1 1 PPM 0.0 4.02 10 PPM 0.2 7.23 100 PPM 0.4 10.44 1000 PPM 0.6 13.65 1% 0.8 16.86 25% 1.0 20.0Figure 2-3: Analog signal output offsetTELEDYNE ANALYTICAL INSTRUMENTS2-7