Hb And Hs Alarms; Theory Of Operation; Alarm Output Operation; Precautions - Omron E5ZD Operation Manual

HB and HS Alarms

3-5

HB and HS Alarms

3-5-1 Theory of Operation

3-5-2 Alarm Output Operation

3-5-3 Precautions

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Either of the E54-CT1 and E54-CT3 Current Transformers can be used with the
E5ZD to detect circuit breaks or shorts (e.g., SSR failures) in the heater. Detec-
tion levels can be set independently for each control point.
The power supply line to the heater is passed through the hole of the Current
Transformer (CT). When AC current then flows though the power supply line, an
AC current will be induced in the CT and can be input to the E5ZD so that the
current flow to the heater can be determined. This allows the E5ZD to detect lack
of current flow when the heater is supposed to be on, resulting in the generation
of an HB (heater burnout) alarm. It also allows the E5ZD to detect current flow
when the heater is supposed to be off, resulting in the generation of an HS (heat-
er short circuit) alarm, as can happen with an SSR failure. The HS alarm output
goes ON when there is a current flow of 0.5 A or more on the CT when the control
output of the E5ZD is OFF.
There is only one output each for the HB and HS alarms. When an error gener-
ated in any control point, the alarm output will be turned ON. Commands can
then be sent from the host computer to determine which control point generated
the error.
For the HB alarm output to be turned ON, the control output must be ON continu-
ously for at least 200 ms. For the HS alarm output to be turned ON, the control
output must be OFF for at least 200 ms. Either of these alarms might be delayed
by up to six times the control period for 4-point models, by up to eight times the
control period for 6-point models, and by up to ten times the control period for
8-point models.
• Activate HB alarm operation only after turning on the power supply to the heat-
er. If the heater is turned on after activation, the alarm output will turn ON.
• The actual current flow to the heater can vary from the rated current. Use the
Heater Current Read Command (RZ) under actual operating conditions to de-
termine appropriate detection levels.
• Allow a margin of at least 1 A between the normal heater current and the detec-
tion level. Smaller differences can result in detection instability.
• Heater burnout detection cannot be used if the heater is controlled through
phased or cyclic control methods.
• The HB and HS alarms cannot be used with 3-phase heaters.
• The HS alarm output will go ON if the control output is OFF and if 0.5 A or more
is flowing through the Current Transformer.
Section 3-5