GHM Messtechnik GmbH – Standort Martens
Kiebitzhörn 18 ● 22885 Barsbüttel ● Germany
Phone +49-40-670 73-0 ● Fax -288
www.ghm-messtechnik.de ● [email protected]
14
Change of the measuring range start value
The start value can be changed by +/-40% based on the factory measuring range
(= factor end value - factor start value).
In order to show the potential change of the start value on the output current
range, a virtual zero point of
12mA
*) is assumed.
This output current is generated in service mode if the
trim
potentiometer is positioned at the calibrated factory setting.
The
trim potentiometer is then in the centre position. The operation LED
illuminates red (continuous light).
*) If the factory zero point were based on 4mA, the output current for the simulation of a reduction by 40% would have to be negative,
which is not technically possible
According to the value range table on the preceding page, for a change of the
start value by
-40%
the output current must be reduced by turning anticlockwise 6.4mA down to
5.6mA (12mA - 6.4mA = 5.6mA)
-10% the output current must be reduced by turning anticlockwise 1.6mA down to
10.4mA (12mA - 1.6mA = 10.4mA)
+10%
the output current must be increased by turning clockwise 1.6mA up to
13.6mA (12mA + 1.6mA = 13.6mA)
+40% the output current must be increased by turning clockwise 6.4mA up to
18.4mA (12mA + 6.4mA = 18.4mA)
The operation LED blinks
green
with a reduction and
red
with an increase.
Note:
The device can only detect a minimum measurement temperature of -50°C in
most measuring ranges (refer to "Technical data" for more information).
Therefore, a reduction of the start value by -40% only makes sense in the factory
measuring ranges of 0..50°C, 0..100°C and -20..40°C. However, since the device
can not recognise the measuring range to be applied later
after leaving the
service mode, a reduction by -40% can always be adjusted in this mode.
In reality the device would switch off the output if the measuring temperature is too
low (approx. 0mA).
Examples
1) A measuring range of 0..500°C should be changed to 0..400°C.
For this purpose, the factory end value must be reduced by 20%
(1 - 400°C / 500°C = 0.20 = 20%).
The value range table on the previous page shows that
in service mode a
reduction of the output current by 3,2mA must take place
.
Therefore, an output current of 16.8mA must be adjusted (20mA – 3.2mA =
16.8mA) in service mode by the
trim potentiometer.
In service mode for the
trim potentiometer the factory setting of 12mA
should be left.
