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EPS Stromversorgung GmbH
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PSI 9000 3U Series
4.4
Calibration
4.4.1 Preface
The devices of series PSI 9000 feature a function to re-adjust the most important output values when doing a
calibration and in case these values have moved out of tolerance. The readjustment is limited to compensate
small differences of up to 1% or 2% of the max. value. There are several reasons which could make it necessary
to readjust a unit: component aging, component deterioration, extreme ambient conditions, high frequent use.
In order to determine if a value is out of tolerance, the parameter must be verified first with measurement tools of
high accuracy and with at least half the error of the PSI device. Only then a comparison between values displayed
on the PSI device and true DC output values is possible.
For example, if you want to verify and possibly readjust the output current of model PSI 9080-510 3U which has 510
A maximum current, stated with a max. error of 0.2%, you can only do that by using a high current shunt with max.
0.1% error or less. Also, when measuring such high currents, it is recommended to keep the process short, in order
to avoid the shunt heating up too much. It is furthermore recommended to use a shunt with at least 25% reserve.
When measuring the current with a shunt, the measurement error of the multimeter on the shunt adds to the error
of the shunt and the sum of both must not exceed the max. error of the device under calibration.
4.4.2 Preparation
For a successful calibration and readjustment, a few tools and certain ambient conditions are required:
•
A measurement device (multimeter) for voltage, with a max. error of half the PSI’s voltage error. That measure
-
ment device can also be used to measure the shunt voltage when readjusting the current
•
If the current is also going to be calibrated: a suitable DC current shunt, ideally specified for at least 1.25 times
the max. output current of the PSI and with a max. error that is half or less than the max. current error of the PSI
device to calibrate
•
Normal ambient temperature of approx. 20-25°C
•
Warmed up PSI unit, which has been run for at least 10 minutes under 50% power
•
One or two adjustable loads, preferably electronic ones, which are capable of consuming at least 102% of the
max. voltage and current of the PSI device and which are calibrated and precise
Before you can start calibrating, a few measures have to be taken:
•
Let the PSI device warm up for at least 10 minutes under 50% load, in connection with the voltage / current source
•
In case the remote sensing input is going to be calibrated, prepare a cable for the remote sensing connector to
DC output, but leave it yet unconnected
•
Abort any form of remote control, deactivate master-slave mode, set device to
U/I
mode
•
Install the shunt between PSI device and load and make sure the shunt is cooled somehow
•
Connect external measurement device to the DC output or to the shunt, depending on whether the voltage is
going to be calibrated first or the current
4.4.3 Calibration procedure
After the preparation, the device is ready to be calibrated. From now on, a certain sequence of parameter calibra
-
tion is important. Generally, you don’t need to calibrate all three parameters, but it is recommended to do so.
Important:
When calibrating the output voltage, the remote input “Sense” on the rear of the device has to
be disconnected.
The calibration procedure, as explained below, is an example with model PSI 9080-170 3U. Other models are
treated the same way, with values according to the particular PSI model and the required load.
