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GEK-86038
Relays to be used with direct current power should be tested using a good
direct current power supply, not full wave rectified power.
Unless the rectified
power supply is well filtered, that is, there is less than 5% ripple, the IRT
auxiliary circuits may behave slightly different when tested with a power supply
that is substantially different than the system power supply.
Since all type IRT relays that are in service operate in their case, they
should be tested in their case or an equivalent steel case.
In this way, any
magnetic effects of the enclosure will be duplicated during testing.
Before testing is begun, check that the relay is level and in a vibration-free
environment.
In addition, the relay should have the cover on and power applied at
rated voltage and frequency to the operating circuit for approximately 30 minutes
prior to actual temperature point testing.
During the 30 minute warm up period,
there should be a simulated RTD load on terminals 4, 5 and 6.
Selection of Simulated RTD Load
To choose the value of this simulated RTD load, select the temperature at
which relay operation is desired.
The relay is calibrated in degrees
centigrade.
Figure 16 may be used to convert Fahrenheit to Centigrade if
temperature is known in Fahrenheit.
Go to Figure 13, 14, or 15, depending
upon the type of RTD for which the IRT relay has been designed (10 ohms at
25oc copper, 100 ohms
@ ooc
platinum, or 120 ohms
@ ooc
nickel).
Select a
resistor value equal to the simulated RTD load resistance associated with the
desired operating temperature.
This is the resistance to be used as the
simulated RTD load.
Measure the resistance of the resistor very carefully,
since a small difference in resistance values can mean several degrees
difference between what is desired and what is actually obtained.
During the 30 minute warm up period, set a temperature on the temperature
selection dial just over the temperature associated with the simulated RTD load.
The relay should not close the IRTL (overtemperature) contact.
Apply power at rated voltage and frequency to the auxiliary circuits.
After the 30 minute warm up period, adjust the temperature selection dial to
the temperature associated with the resistance of the simulated RTD load.
The
relay overtemperature contact (IRTL) should close within 2° of the relay setting.
If it does not, see the CALIBRATION PROCEDURE section.
The IRT51F, IRT51G and IRT51H relays have a reset temperature contact (IRTR).
When the relays are shipped from the factory, the reset temperature is adjusted to
100C below the temperature dial selection temperature.
To change this reset
temperature, the contact gap distance must be changed by loosening the locking
screws of the low temperature contact dial, and turning the dial.
Turn the dial
counterclockwise (opening the contact gap) to decrease the reset temperature, or
turn it clockwise (closing the contact gap) to raise the reset temperature.
Tighten the locking screws after adjusting the contact gap.
To check the reset
temperature setting, choose a simulated RTD resistance that corresponds to the
desired reset temperature.
The IRTR (reset) contact should close within 20of the
desired reset temperature.
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Rev1sed s1nce last issue
17
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