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The front panel display on the 7500/7600/7550/7650 meters automatically scales to display voltage, current, and energy readings in appropriate units.
The displayed units cannot be changed because they are based on the CT / PT ratios.
The User Guide mentions these 'Automatic Units' but does not explain how to change the CT / PT ratios to obtain the desired units.
ION 7500 / 7600 / 7550 / 7650
Changing scale on meter.
The meter automatically scales the reading to the appropriate units; sometimes this is not desired as the precision of the reading may be lost.
The meter assumes that the user has entered the correct PT and CT ratio range for the desired scaling unit.
To change the way the meter scales voltage, current and power, adjust the PT or CT primary parameters as follows:
For V or A: Make PT or CT Primary < 1000
For KV or KA: Make PT or CT Primary within 1000 to 1,000,000
For MV or MA: Make PT or CT Primary > 1,000,000
For W: (CT*PT*3/1000) < 1000
(CT*PT) < 333,333
For KW: 1000 < (CT*PT*3/1000) < 1,000,000,
333 < (CT*PT) < 333,333
For MW (CT*PT*3/1000) > 1,000,000
(CT*PT) > 333,333
NOTE: After scaling the PT PRIMARY, also scale the PT SECONDARY appropriately.
If the actual PTs are 4160:120 and you want to display KV instead of V (i.e. 4.26 KV) set PT PRIMARY to 416 and PT Secondary to 12.
- If these changes are made from the front panel, note that you will have to do each one separately. During this time the meter will calculate 'wrong' values.
For example, using the case above, if you first changed the PT primary to 416, and then changed the secondary to 12, as soon as you make the first change (but before you make the second) the effective PT ratio becomes 416:120. The calculated values in the meter for volts, power and energy will be 1/10th their actual values. This is corrected as soon as you make the change to the secondary value. This will affect the following functions (and maybe a couple others as well):
- Voltage and Power Minimums will likely drop to 1/10th their nominal levels
- Sag/Swell module will 'detect' a drop in voltage, trigger a waveform capture and create an event which will alarm in ION/SPM/PME.
This can be avoided by first disabling the sag/swell detection (either in Vista, or from the front panel by setting the Nominal Voltage to zero before making any other changes).
- Any Setpoints configured for voltage, current or power could be triggered.
- If the changes were performed using ION Designer, all parameters can be changed simultaneously, avoiding the mentioned effects.