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50 Micro Motion 7827 Digital Viscosity Meter
General Maintenance
6. Check that the Signal Converter is providing adequate power to the meter and that the Signal
Converter itself is functioning properly.
Check calibrations should be carried out at specified intervals in order to highlight a malfunction or
deterioration in meter performance. If a fault or a drop in performance is discovered, further tests – as
described in "fault analysis" below – are required to identify the cause of the fault. When a fault has
been traced, actions to rectify the fault may include making good any poor connections, replacing the
amplifier board, or in extreme cases the complete meter, Signal Converter, or both.
(For details of carrying out a check calibration, refer to Chapter 6).
7.3 Fault analysis
A fault may be described as falling in one of three categories:
• Readings unsteady
Normally caused by the presence of gas bubbles around the tines. Severe electrical
interference, severe pipeline vibrations, electrical and electronic faults can also cause this
effect.
• Readings outside limits
Normally caused by deposition and/or corrosion on the tines. Electrical and electronic faults
can also cause this effect.
• Readings not updating
Normally caused by memory locations within the Signal Converter being SET when they
should be FREE and by wiring open circuits between Signal Converter and meter.
Checking values in Signal Converter locations is easier than checking electrical power consumption,
which in turn is easier than physical inspection, so faults should therefore be considered in this order.
7.3.1 Checking the Signal Converter
All of the 7827 meter's results are compiled from four main parameters:
• Time period A (τ
A
)
• Time period B (τ
B
)
• Temperature from the PRT
• Quality factor (Q) is obtained from τ
A
& τ
B
Hence, if instability or inaccuracy of the indicated viscosity or density exists, these parameters should
be checked first.
Error on indicated viscosity
If the indicated viscosity is in error, follow the table below and, if necessary, refer to the other tables
later in the chapter to find the cause of the fault.