8. THE ALARM LED
Alarm LED
(AL)
lights in cases:
• exceeding of
permissible measurement range
• detection of sensor malfunction (shortcut or break of measurement circuit)
9. 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 50mA (typical).
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).
10. DISPLAYED VALUES CALCULATION
For simplicity of examples it's assumed that current input is selected, and all calculations are related to this
input. When voltage input is selected calculations are similar (be sure of particular ranges and units).
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 (0 mA for 0-20mA range, and 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 20mA for 0-20mA range, and 16mA for 4-20mA range). So normalized result can be expressed by
expressions:
10.1. 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.
where I
inp
. Means input current (in mA), and In – normalized result.
If measured value exceeds the nominal input range (0-20mA or 4-20mA), and do not exceed the
permissible input range, then received normalized In 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.
I
I
I
I
38
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