Schweitzer Engineering Laboratories SEL-787 - Table 4.36 Summary of Steps

4.86
SEL-787 Relay Instruction Manual Date Code 20081022
Protection and Logic Functions
Global Settings (SET G Command)
Signal offset compensation factor calculation procedure:
1. Turn the SEL-787 on and allow it to warm up for a few
minutes.
2. Set the analog inputs for each analog channel to the desired
range using the AIxxxTYP, AIxxxL, AIxxxH, AIxxxEL, and
AIxxxEH settings (for example, ±1 mA).
3. Short each analog input in turn at the device terminals using
short, low resistance leads with solid connections.
4. Issue the command MET AI 10 to obtain 10 measurements for
each channel.
5. Record these 10 measurements, then calculate the average of
the 10 measurements by adding the 10 values algebraically, and
dividing the sum by 10. This is the average offset error in
engineering units at zero input (for example, –0.014 mA).
6. Negate this value (flip the sign) and add the result to each of the
AIxxxEL and AIxxxEH quantities. For this example, the new
AIxxxEL and AIxxxEH values are –0.986 mA and 1.014 mA.
Analog Input Setting Example
Assume we installed an analog card in Slot 3. On Input 1 of this analog card,
we connect a 4–20 mA transducer driven from a device that measures
temperature on a transformer load tap changer mechanism. For this
temperature transducer, 4 mA corresponds to –50°C, and 20 mA corresponds
to 150°C. You have already installed the correct hardware jumper (see
Figure 2.3 for more information) for Input 1 to operate as a current input.
Table 4.36 summarizes the steps and describes the settings we will carry out in
this example.
Ta b l e 4 . 3 6 S um m ar y of Ste p s
Step Activity Terse Description
General
1 SET G
AI301NAM
Access settings for INPUT 1
2 TX_TEMP Enter a Tag name
3 I Select type of analog input; “I” for current
Transducer
High/Low
Output
4 4 Enter transducer low output (LOW IN VAL)
5 20 Enter transducer high output (HI IN VAL)
Level
6 Degrees C Enter Engineering unit
7 –50 Enter Engineering unit value LOW
8 150 Enter Engineering unit value HIGH
Low Warning/
Alarm
9 OFF Enter LOW WARNING 1 value
10 OFF Enter LOW WARNING 2 value
11 OFF Enter LOW ALARM value
High Warning/
Alarm
12 65 Enter HIGH WARNING 1 value
13 95 Enter HIGH WARNING 2 value
14 105 Enter HIGH ALARM value