Pentair 920 Series Installation, Operating And Maintenance Instructions page 38

INDUSTRIAL HEAT TRACING SOLUTIONS
before the corresponding alarm will be indicated.
• If the user resets an alarm while the alarm condition is still exists, the alarm will not be
indicated again until the entire alarm filter time has expired.
3.8.16 nomInaL resIstanCe settInG
purpose: This parameter defines the nominal expected heater resistance. A value must be
entered by the user to allow the HIGH and LOW RESISTANCE ALARMS to be used. In installations
where the power source may experience periodic fluctuations (surges and/or brown-out con-
ditions), alarming on resistance deviation offers an improved method of monitoring tracer integrity
over simple LOW and HIGH CURRENT ALARMS. Since the ratio of voltage to current is monitored,
the HIGH and LOW RESISTANCE ALARMS offer cable monitoring that is relatively immune to
voltage fluctuations.
range: 2.00 to 2000.00 Ω
procedure: The NOMINAL RESISTANCE value can only be set if either the LOW RESISTANCE and/
or the HIGH RESISTANCE ALARMS are enabled. Once the controller and the heating cable have
been installed, the following procedure should be used to determine the NOMINAL RESISTANCE
setting:
• Adjust the CONTROL SETPOINT temperature to turn on the output switch.
• Allow the load to come up to design temperature and its power consumption to stabilize.
• Using the 920 Operator Console, access the RESISTANCE reading and record its value. Return
the CONTROL SETPOINT temperature to its proper setting.
• Enter the recorded resistance value as the NOMINAL RESISTANCE setting.
Important: The setup procedure outlined above may have to be repeated a number of times
to arrive at a correct nominal resistance setting. This value will be affected by the heating cable
temperature, which in turn is affected by ambient temperature, insulation level, a full or empty
pipe or vessel, etc.
3.8.17 overCurrent trIp aLarm (ssr onLy)
purpose: The overcurrent trip feature is always enabled when using an SSR output switch and is
used to provide protection for the output switch. Enabling this alarm will only inform the user of an
excessively high current condition and that the output switch has been latched off. During a high
current condition, the controller attempts to soft start a heating cable by a technique involving
measured in-rush current and the SWITCH CURRENT RATING. If the controller is unable to start
the cable, it will eventually trip its output switch off and will not retry or pulse its output switch
again. At this point the OVERCURRENT TRIP ALARM is latched on.
Important:
• The controller is not a safety cutout or an overcurrent protective device as defined by the
National and Canadian Electrical Codes (NEC and CEC). A protective device such as a circuit
breaker or fuse must be included as part of a proper design and be selected in accordance with
the requirements defined in the National Electrical Code (NEC) and/or the Canadian Electrical
Code (CEC).
• The controller cannot protect the SSR from short circuits or excessive overcurrent conditions.
Always ensure that the power is off prior to performing any maintenance or troubleshooting of
the heating circuit. Verify that no damage has occurred to the cable or the controller prior to
re-energizing the circuit.
alarm mask: ENABLE or DISABLE
procedure: Adjust the SWITCH CURRENT RATING setting to the actual current rating of the SSR.
Enable or disable the alarm as required. Note that the OVERCURRENT TRIP ALARM does not have
to be enabled in order to adjust the SWITCH CURRENT RATING setting.
Important: This alarm should be left enabled since an overcurrent trip condition would
normally represent a serious problem. This is a fac-tory-set alarm value and disabling the alarm
does not disable the overcurrent trip function. In some applications the use of self-regulating
cables will produce very high in-rush currents during cold startup. These currents may exceed
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