Part 2

Plug-In Assembly Configuration 385Software CompensationAs factory configured, the assembly is set for software compensation. With softwarecompensation, a reference junction transducer measures the voltage of anisothermal block. The voltage measured is a function of the temperature of the blockand is connected to channel B9 (channel 191 as shown in Figure 80.Thus, with software compensation, only 19 channels are available for inputs, sincethe 20th channel (B9) is dedicted to the reference junction transducer circuits.However, you can use a mix of thermocouples on a single assembly.Hardware CompensationSoftware compensation has the advantage of being able to mix various types of thermocoupleson a single assembly. However, the measurement process is rather slow,since the reference voltage on channel 19 should be measured frequently to avoidisothermal block temperature drift errors.If you have only one type of thermocouple to measure, the assembly can be configuredfor hardware compensation and thermocouple voltages can be measureddirectly. With hardware compensation, the reference junction transducer is removedfrom the circuit and 20 channels can be used for input.For hardware compensation, the compensation voltage is determined by two resistorsinstalled on the terminal card, whose value is dependent on the type of thermocouplebeing measured. Thus, the voltage displayed on the front panel or at the controlleris the true (compensated) thermocouple voltage and can be directly used with a standardlook up table to determine equivalent temperature.SpecificationsSpecifications for the 20 channel relay multiplexer assembly with thermocouple compensationfollow. Specifications are performance standards, or limits, against whichthe assembly may be tested.OPTION 020RELAY MULTIPLEXER ASSEMBLY WITHTHERMOCOUPLE COMPENSATIONReference Junction Compensation ComparisonCompatibleThermocouplesCompensation TypeSoftwereHardwareMeasurement ChnnnelsAvailable per AssemblyReference JunctionCompensation Accuracy 1 "C(23OC + 5OCIFollowing Types:B.E.J.K.R.S.TValid for thermocouple compensation only. The total accuracy of349 7A based temperature measurement systems including compensationaccuracy, 3497A scanner offsets. DVM accuracy andsoftware accuracy is shown below.Temperature Coefficient(O°C - 18OC.28OC - 55°C).009°C/oCStability.075°C11000 HoursTemperature OifferenceAcross Isothermal < .ZoC IBlock:1Output:11 OOrnVlOC1 1(Channel B9)2.5V@25"CAdditional In Series~esistance: IOQ(Hardware Cornpensasationonly).1 Software Com~ensation I I IArtisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com