Chapter 8. Maintenance and TroubleshootingModel PM880 Portable Hygrometer User’s Manual 1578.12 Common ProblemsIf the PM880 measurement readings seem strange, or they do not makesense, there may be a problem with the probe or a component of the processsystem. Table 6 contains some of the most common measurement problems..Table 6: Troubleshooting Guide for Common ProblemsPossible CauseSystemResponse ActionSymptom: Accuracy of moisture sensor is questioned.Insufficient time for systemto equilibrateDewpoint at sampling pointis different than the dew-point of the main stream.Probe reads toowet in dry downconditions, ortoo dry in wetup conditions.Probe reads toowet or too dry.Change the flow rate. A change in dewpointindicates the sample system is not at equi-librium, or there is a leak. Allow sufficienttime for sample system to equilibrate andmoisture reading to become steady. Checkfor leaks.Readings may be correct if the samplingpoint and main stream do not run under thesame process conditions. The differentprocess conditions cause readings to vary. Ifsampling point and main stream conditionsare the same, check sample system pipes,and any pipe between the sample systemand main stream for leaks. Also, checksample system for adsorbing watersurfaces, such as rubber or plastic tubing,paper-type filters, or condensed water traps.Remove or replace contaminating partswith stainless steel parts.Sensor or sensor shieldaffected by processcontaminants(refer to Application of theHygrometer).Probe reads toowet or too dry.Clean the sensor and the sensor shield asdescribed inAluminum Oxide Probe Maintenancein Application of the Hygrometer.Then reinstall the sensor.Sensor is contaminated withconductive particles(refer to Application of theHygrometer).Probe readshigh dewpoint.Clean the sensor and the sensor shield asdescribed in Aluminum Oxide Probe Main-tenance in Application of the Hygrometer.Then reinstall the sensor.
