| Symptom | Possible cause(s) | Action |
|---|---|---|
| readings slowly changing or dithering |
sensor is not at same temperature as fluid | allow time for sensor to reach the fluid temperature |
| transducer not properly mounted | ensure process fitting is properly tightened | |
| jitter in the readings | intense external vibration | apply filter (see signal processor User Manual) |
| readings higher or lower than expected |
non-Newtonian fluid* | apply SPAN factor (see signal processor User Manual) |
| temperature higher or lower than assumed | check fluid temperature | |
| readings do not match measurements made by other viscometer | fluids at different temperatures | ensure all measurements are made at the same temperature |
| fluid properties change between readings | verify that the properties and composition of the fluid “seen” by the reference viscometer match those of the fluid measured by the XL7 | |
| non-Newtonian fluid* | apply SPAN factor (see signal processor User Manual) | |
| reference viscometer has not been calibrated or maintained properly | check calibration of reference viscometer | |
| operating parameters do not match | verify units of measurement | |
| sensor tip and shaft not fully immersed in fluid | ensure shaft is fully immersed | |
| fluid density has not been accounted for |
enter correct value of fluid density (see relevant signal processor User Manual for procedure) | |
| integral temperature sensor readings not showing on display | transducer and signal processor settings incorrect | verify input settings for both transducer and signal processor (see relevant signal processor User Manual for details) |
* Explanation:
The XL7 operates at very high shear rates. Generally, most non-Newtonian (shear-rate dependent) fluids are “shear-thinning”, i.e. the apparent viscosity decreases with increasing shear rate. The high shear rate of the XL7 will therefore give a lower viscosity reading than low-shear devices such as flow cups or rotational, capillary or falling-ball viscometers. However, repeatability is maintained, even in very non-Newtonian fluids, and the sensor will accurately track any changes in fluid viscosity.
Looking for VP550 troubleshooting? See 'using your viscometer' help section here >