User manual - METER SWE-73-L
8.
OVER-CURRENT PROTECTION
The current input of the device is equipped with over-current protection circuit. This circuit
protects the standard resistor to damage. Maximum input current is set to about 50 mA.
When temperature of the standard resistor falls, the protection circuit will turn off himself
automatically, and the device will measure the input current again. Due to thermal
phenomenon in the standard resistor, precision of the measurement may be lower, during few
minutes (up to the standard resistor temperature will falls to the environment temperature).
9.
DISPLAYED VALUES CALCULATION
The first step to compute the result of measure is the calculation of the normalized result
(it means result of 0-1 range). To do it, the begin of the input range (4mA for 4-20mA range)
must be subtracted from measured value. Next, received result must be divided by the width of
the input range (it means 16mA for 4-20mA range). So normalized result can be expressed by
expressions:
I
n
=
I
inp.
−
4
16
for
4
÷
20
mA range
where I
inp.
Means input current (in mA), and I
n –
normalized result.
If measured value exceeds the nominal input range (4-20mA), and do not exceed
the permissible input range, then received normalized I
n
result will exceed 0-1
range, e.g. input range 4-20 mA, input current = 3 mA – the normalized result is
equal -0,0625, and for input current = 22 mA, the normalized result is equal 1,125.
In such cases presented expressions are still correct.
9.1.
ADDITIONAL CALCULATIONS (USED CONVERSION CHARACTERISTIC)
The manner of the additional computation of the displayed result depends on selected
conversion characteristic. All presented charts are connected with the input range 4 - 20 mA.
25
i
