LTH Electronics HPT63, Руководство по эксплуатации

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14 Fault Finding
41
♦
Where practical check the temperature sensor resistance against the table
in Appendix E – Temperature Sensor Data.
Current Output is Incorrect or Noisy
♦
Check that the maximum load resistance for the current loop has not been
exceeded. (1000
Ω
). Maximum load resistance is related to the supply voltage
by the equation R
max
= (V
supply
-2)/0.04.
♦
Check that the terminals have been wired correctly (see Section 3.4
Connections ).
♦
Check that the cable screen is attached to Earth at one end, and that the
cable does not pass too close to a power cable (see
Section 2.2 Noise
suppression ).
♦
Check that
t
he current output has been configured properly (see Section
10.7
Current Output Calibration ).
Relays Appear to Malfunction
♦
Check that the unit is On-Line (see Section 10.1 On-Line/Off-Line Operation )
♦
Check that the set point configuration is correct (see Section 8 Set Point
Relays )
♦
If the relays are vibrating or ‘chattering’ as they pass the set point, check the
hysteresis setting (see
Section 8.3.1 On/Off Mode ) and increase if necessary.
♦
Ensure that the relays are connected properly (see Section 3.4.7 Relay
Connections ) and that the voltage/current levels are not exceeding the
specification (see Section 1.2 Unit Specification ).
♦
Check that the instrument input cables are not picking up excessive noise,
(see
Section 2.2 Noise suppression ).
A Bell Symbol is Flashing on the Display
The system has detected an error but the error messages have been disabled in the
Configuration menu (See Section 12.3 Error Messages ). Enable the error
messages, correct the error and then disable the error messages only if absolutely
necessary.
14.1 Problems with Cables and Connectors
The cable connecting the pH electrode to the instrument is the most common cause
of problems in pH measurement systems. The importance of the following
recommendations cannot be over stressed.
Input Resistance
The high input resistance, required for the optimum performance from a pH electrode
system, will be seriously degraded if any grease, dirt, or dampness is allowed to