Omron E5ZD, Руководство по эксплуатации

Страница: 69 / 157

59
3-5-4 Application Example
The following example shows the setup required to turn ON the HB alarm output
when there is a circuit break in any one of three 200-VAC, 2-kW (rated current:
10 A) heater circuits wired in parallel. This situation is as illustrated below.
Heater circuits
Three 2-kW circuits
Relay driven by control output
200 VAC
Current Transformer
To E5ZD’s CT input terminals
Wiring to E5ZD
Current Transformer
Heater power supply line
1, 2, 3... 1. First the heater, Current Transformer, and E5ZD are wired. (The wiring
from the Current Transformer to the E5ZD is not polarity sensitive.)
2. Because the rated current is 10 A for one heater circuit, the three circuits
draw 30 A. If one circuit breaks, the remaining two would draw 20 A.
3. Although here it is necessary to generate an alarm whenever the current
drops below 30 A, caution is required due to the current changes that can
result from changes in the power supply voltage. If we assume a maximum
voltage fluctuation of 10%, the maximum current fluctuation would also be
10%. The minimum current for when all three circuits are operating and the
maximum current when one of the three circuits is broken can thus be cal-
culation as follows:
Minimum for 3 circuits = 30 A
×
(1 – 0.1) = 27 A
Maximum for 2 circuits = 20 A
×
(1 + 0.1) = 22 A
4. The detection level for heater burnout can thus be set midway between
these points, at 24.5 A. (i.e., (27 A + 22 A)/2).
5. To prevent erroneous detection, the heater circuits need to be turned on
before the detection operation is activated.
HB and HS Alarms
Section 3-5