GHM Messtechnik GmbH – Standort Martens
Kiebitzhörn 18 ● 22885 Barsbüttel ● Germany
Phone +49-40-670 73-0 ● Fax -288
www.ghm-messtechnik.de ● info@martens-elektronik.de
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2) A measuring range of 0..100°C should be changed to -25..60°C.
For this purpose, the measuring range end value must be reduced by 40%.
(1 - 60°C / 100°C = 0.4 = 40%)
Based on the value range table on page 13, the output current must be
reduced (in service mode) by 6.4mA for a reduction of the end value by 40%.
Therefore, an output current of 13.6mA must be adjusted (20mA – 6.4mA =
13.6mA) with the
trim potentiometer.
To calculate the adjustment for the measuring range start value, the factory
measuring range is determined first (factory end value - factory start value):
100°C – 0°C = 100°C.
(negative start values must be added because of the double sign)
The measuring range start value should then be reduced by 25°C based on the
measuring range, which then also necessitates a reduction of the output current
by 25% in service mode.
This value is multiplied by the greatest possible current change of 16mA: 16mA
* 25% = 4mA
Therefore, an output current of 8mA must be adjusted in service mode for the
trim potentiometer.
(virtual zero point at 12mA minus 4mA reduction = 8mA)
Accuracy
A reduction of the end value or an increase of the start value always reduces the
measuring accuracy.
The (in)accuracy values specified in the "Technical data" thus increase by the
factor:
factory end value – factory start value
(divided by)
(adjusted end value) – (adjusted start value)
(negative start values must be added because of the double sign)
4.23 Current simulation
The change of the output current proportional to the trim potentiometer setting in
service mode can also be used to simulate an action which should appear in
normal mode.
An output current in the range of
5.6mA to 18.4mA can be simulated
with the
potentiometer.
The
potentiometer can
simulate an output current in the range of 10mA to
20mA
.
After the simulation, the potentiometers must then be turned back to the original
position, i.e. the factory setting.
