Calibration Utility Manual
Revision 1.0
Full Version
September, 2010
File: MAN-0086R1.0, GSC400 Calibration Utility Manual.doc,
GSC400
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This Document
This document will explain the GSC400 AC calibration process and how to use
the GSC400 Calibration Utility to perform calibrations in the field.
Table of Contents
1. Calibration Theory................................................................................................ 3
2. GSC400 Calibration Process ............................................................................. 5
2.1 Definitions.......................................................................................................... 6
2.2 AC Current Slope Calculation........................................................................ 6
2.3 AC Voltage Slope Calculation........................................................................ 6
2.4 AC Current Offset Calculation........................................................................ 7
2.5 AC Voltage Offset ............................................................................................ 7
3. GSC400 AC Calibration Utility ........................................................................... 8
3.1 Main Screen...................................................................................................... 8
3.2 Manual Calibration........................................................................................... 9
3.3 Calibration Wizard.......................................................................................... 10
3.3.1 Equipment ................................................................................................... 11
3.3.2 Wizard Walk Through................................................................................ 12
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1. Calibration Theory
In an ideal world the output from the AC sensing circuit would be proportional to
the AC current and voltage at its input for all voltage and current levels (within a
certain random accuracy).
In practice, the un-calibrated accuracy can vary as a function of the voltage or
current level (this is called a slope error) and/or be offset by a fixed amount
(offset error). This is shown in Figure 1 to Figure 3 below.
The point of calibration is to make the measured current and voltage equal to the
input voltage and current within a certain random error tolerance.
Precalibrated
Pivot Poin t
curve
In put V olt a ge/Cu r r ent
In put V olt a ge/Cur rent
Error varies with
volt age/c ur r ent lev el.
Measured V oltage/Cur r ent
Figure 1 – Pure slope error.
C o nstant er r or
Ide al Curve
Precalibrated
curve
Ideal Curve
Measured V oltage/Cur r ent
Figure 2 – Purse offset error.
In put Voltage/Curr ent
Pivot Point
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Precalibrate
d cur v e
Ideal
Curve
Measured Voltage/Current
Figure 3 – Offset and slope errors.
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2. GSC400 Calibration Process
During manufacture the GSC400 AC sensing is calibrated. The GSC400
contains slope and offset constants for each of the phases (A, B, and C) for
voltage and current (12 constants in total). These constants can vary from -126
to 126.
Factory Calibration Steps
1. Measure voltage/current at two points. Use values to determine the
actual slope. Plug this into an equation to determine the voltage and
current slope constants for each phase. Update the controller with these
constants.
2. The calibration at the factory repeats this process and adds the two slope
constants to obtain the final slope constant to ensure the slope is as
accurate as possible. Once this is performed there only a pure offset
error remains. In practice there is always a small slope component
present.
3. Measure two current/voltage points and take weighted average.
Determine the offset error. Plug this into an equation to determine the
voltage and current offset constants for each phase. Update the
controller with these constants.
4. Verify the AC voltage and current meet the accuracy tolerance
specifications.
Calibration Points
AC Voltage: 110VAC, 220VAC
AC Current: 0.8A, 4A
Note: This is current into GSC400, 0 to 5A. This gets multiplied by CT ratio for
display on controller)
Field Calibration
In the field for AC current it is possible to apply the above procedure as the
current can be varied.
For AC voltage this is not possible since the voltage cannot be varied. For
voltage only an offset calibration can be performed and there will still be a slope
error component after the calibration. This means as the actual voltage varies
from the calibrated voltage point the accuracy of the GSC400 will decrease.
The sections below will outline the equations used in the calibration of the
GSC400.
2.1 Definitions
ACC_MH – AC Current Measured High
ACC_ML – AC Current Measured Low
ACV_MH – AC Voltage Measured High
ACV_ML – AC Voltage Measured Low
ACC_RH – AC Current Reference High
ACC_RL – AC Current Reference Low
ACV_RH – AC Voltage Reference High
ACV_RL – AC Voltage Reference Low
LOW_CUR_WEIGHTED_AVG – 5
LOW_VOL_WEIGHTED_AVG – 2
ACC_S – AC Current Slope
ACV_S – AC Voltage Slope
ACC_O – AC Current Offset
ACV_O – AC Voltage Offset
2.2 AC Current Slope Calculation
slope = (ACC_MH – ACC_ML) / (ACC_RH – ACC_RL)
If slope < 0.78 Then
ACC_S = -126
Else If slope > 1.4 Then
ACC_S = 126
Else
ACC_S = (1 - (1 / slope) * 440
End If
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2.3 AC Voltage Slope Calculation
slope = (ACV_MH – ACV_ML) / (ACV_RH – ACV_HL)
If slope < 0.929 Then
ACV_S = -126
Else If slope > 1.083 Then
ACV_S = 126
Else
ACV_S = (1 - (1 / slope)) * 1651
End If
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2.4 AC Current Offset Calculation
offset = -((ACC_ML – ACC_RL) * LOW_CUR_WEIGHTED_AVG + (ACC_MH –
ACC_RH)) / (LOW_CUR_WEIGHTED_AVG + 1)
If offset < -0.252 Then
ACC_O = -126
Else If offset > 0.252 Then
ACC_O = 126
Else
ACC_O = offset / 0.002
End If
2.5 AC Voltage Offset
offset = -((ACV_ML – ACV_RL) * LOW_VOL_WEIGHTED_AVG + (ACV_MH) –
ACV_RH)) / (LOW_VOL_WEIGHTED_AVG + 1)
If offset < -12.6 Then
ACV_O = -126
Else If offset> 12.6 Then
ACV_O = 126
Else
ACV_O = offset / 0.1 ' comment: 1 unit = 0.1V
End If
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3. GSC400 AC Calibration Utility
3.1 Main Screen
When you open the GSC400 AC Calibration Utility the window in Figure 4 will
appear. This window allows you to read or modify the 12 AC Sensing calibration
constants on the GSC400. Each value can range from -126 to 126.
It is highly recommended that you read and record the calibration
constants (click the Read Calibration button shown in the figure below)
before making any changes. Once you make a change it is non reversible.
To read the calibrations click the large “Read Calibration” button. To change a
calibration constant enter the desired values in the boxes and click the “Set”
buttons beside each phase. Make sure that you have the correct COM port
selected under “Communication” menu at the top.
Figure 4 – Calibration Utility Main Window
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3.2 Manual Calibration
AC Voltage Calibration
If the voltage only varies a little from the system voltage a simple offset
adjustment is sufficient. When the voltage offset calibration constant is
decremented by 1 the actual voltage reading is decremented by 0.1VAC. The
calibration constants range from -126 to 126.
If adjusting the voltage offset is not enough the voltage slope calibration
constants can also be adjusted. Increasing the value of the slope constants
decreases the value of the voltage reading.
AC Current Calibration
It is recommended to use the wizard to calibrate the current. See below.
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3.3 Calibration Wizard
Under the “Tools” menu there is a “Calibration Wizard” option that you can use to
automatically calibrate the current.
necessary.
Only perform a calibration if absolutely
Figure 5 – Calibration Wizard Main Window
Click on the Advanced Settings button and check which calibration you wish to
perform (refer to Figure 6 below). Once you are done click on the “X” in the top
right corner to close the window.
1.
Voltage and Current – Performs a slope and offset calibration of
current using two reference AC currents that you supply and an offset
calibration of AC voltage. Do not use if AC voltage tolerance is
adequate.
The old calibration constants stored in the GSC400 are used as a
starting point. If voltage and/or current sensing are significantly off you
should perform a manual AC voltage calibration and then use the
wizard to calibrate the AC current (set all AC current calibration
constants to 0 and select the “Current Only” option before beginning).
If you only have a problem with the AC voltage sensing it is better to
perform a manual calibration. See section 3.2 for instruction on
performing a manual calibration of voltage.
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Current Only – Does not modify the AC Voltage calibration constants.
2.
Figure 6 – Advanced Settings Window
3.3.1 Equipment
If you are doing an AC current calibration you will need the following:
1. An accurate instrument (e.g. ammeter or multimeter set to AC current) to
measure current from the generator. Measure as close to the CTs as
possible.
2. A load source to generate two different currents for the calibration
preferably at 25% and 75% of normal maximum load.
3. Knowledge of the number of phases the GSC400 is measuring (A, B, C).
To determine this look at the AC Voltage connections on the back of the
GSC400.
If you are doing an AC voltage calibration you will need the following:
1. A voltmeter to measure the voltage at the GSC400 terminals.
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3.3.2 Wizard Walk Through
This section will walk you though the wizard steps so you’ll know what to expect.
During the calibration you will be required to measure the load current and enter
it into the wizard. Ideally the load current should be steady to obtain a good
calibration but if not you can try averaging the current readings.
1. At the welcome screen click Next.
You will see the window to the
right.
If you are doing a current only
calibration enter any non-zero
number into the boxes for the
phases that the GSC400 senses.
If you are doing a voltage
calibration you will need to
measure the voltage for each
phase and enter it into each box (it is
important that you enter zero for the
phases not sensed by the GSC400 or the wizard will attempt
calibration for that phase).
Click Next.
2. You will be asked to place the
controller in the OFF mode. You can
ignore this for GSC400 firmware
versions 2.00 and above.
Press OK.
The Utility will get the CT ratio.
Figure 7
Figure 8
3. If the GSC400 is not already in the
RUN mode place the GSC400 in
the RUN mode and wait until AC
voltage reading stabilized.
Click OK.
The utility will then read the
generator voltage.
4. Finally click Next.
5. Out of the two AC currents
(loads) you picked for
calibration place the smaller
load on the generator and
measure the actual current.
Record the current in the utility.
Click Next.
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Figure 9
Figure 10
Figure 11
6. The utility will get the GSC400
measured current.
Click Next.
7. Out of the two AC currents
(loads) you picked for calibration
place the larger load on the
generator and measure the
actual current.
Record the current in the utility.
Click Next.
8. The utility will get the GSC400
measured current.
Click Next.
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Figure 12
Figure 13
Figure 14
9. The utility will calculate the
calibration slope constants
and save them to the
GSC400.
Click Next.
10. Out of the two AC currents
(loads) you picked for
calibration place the smaller
load on the generator and
measure the actual current.
Record the current in the
utility.
Click Next.
11. The utility will get the GSC400
measured current.
Click Next.
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Figure 15
Figure 16
Figure 17
12. Out of the two AC currents
(loads) you picked for
calibration place the larger
load on the generator and
measure the actual current.
Record the current in the
utility.
Click Next.
13. The utility will get the
GSC400 measured current.
Click Next.
14. The utility will calculate the
offset calibration constants
and save them to the
GSC400.
Click Next.
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Figure 18
Figure 19
Figure 20
15. Calibration is finished.
You can select and copy the
text in the box if you want a
copy of the calibration
information.
Click Finish.
Figure 21
Below is an example of the calibration status box text.
Calibration is finished. Click the Finish button to exit.
Click Next to continue.
Offset calibrations stored successfully.
-------------------------------Voltage - Phase C Offset Calibration: 0
Voltage - Phase B Offset Calibration: 0
Voltage - Phase A Offset Calibration: 0
Current - Phase C Offset Calibration: 0
Current - Phase B Offset Calibration: 0
Current - Phase A Offset Calibration: -1
-------------------------Click Next to continue.
Current for phase A, B, and C are: 0A, 0A, and 0A.
Reading current...
Click Next.
Set the load to the high point and enter the current in the box above.
--------------------------------Click Next to continue.
Current for phase A, B, and C are: 0.1A, 0A, and 0A.
Reading current ...
Click Next.
Set the load to the low point and enter the curent in the box above.
-------------------------Click Next to continue.
Slope calibrations stored successfully.
Current - Phase C Slope Calibration: -29
Current - Phase C Delta Slope Calibration: 0
Current - Phase B Slope Calibration: 55
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Current - Phase B Delta Slope Calibration: 0
Current - Phase A Slope Calibration: -126
Current - Phase A Delta Slope Calibration: -3960
-------------------------------Click Next to continue.
Current for phase A, B, and C are: 0.1A, 0A, and 0A.
Reading current ...
Click next.
Set the load to the high point and enter the curent read in the box above.
---------------------------Click Next to continue.
Current for phase A, B, and C are: 0.1A, 0A, and 0A.
Reading current ...
Click next.
Set the load to the low point and enter the value read in the box above.
---------------------------Press next to continue.
Voltage for phase A, B, and C are: 116.2V, 116V, and 115.7V.
Reading system voltage...
Start the Engine/Generator and click OK once the Generator is running.
Current CT ratio: 100A:5A
Getting CT Ratio.
Make note of these in case you need to revert back.
Current slopes for phases A, B, and C are: -126, 55, -29.
Current offsets for phases A, B, and C are: 0, 0, 0.
Voltage slopes for phases A, B, and C are: 18, 18, 25.
Voltage offsets for phases A, B, and C are: 0, 0, 0.
Getting calibration coefficients..
Place the controller in the Off Mode. Click OK once in the Off Mode.
Click the Next button to continue once the voltages are entered.
Enter the voltages for Phase A, B, and C in the boxes above.
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