KROHNE BM 100A Handbook - Manual (Page 42)

42 Handbook BM 100 A
Level measurement: Level pulse amplitude and threshold
After connection to a power supply, the BM100 A will:
1. Measure reflection pulses in terms of voltage amplitude by cycling through a set of gains.
2. Identify the highest amplitude as being the product level.
The diagram below shows a level threshold of 2.71 Volts for a Gain of 1.
1 Initial pulse
2 Flange reflection (except
coaxial probe)
3 Non-product reflection
(e.g. parasite : agitator)
4 Product level reflection
5 Level threshold (with 2
metre steps). Set in user
function 1.5.1.
6 Offset (see below for
definition)
7 Distance measured as a
function of time
Offset is the distance measured as time for the signal to travel from the signal converter to the
flange (the gauge’s reference point).
If difficulties are experienced finding the correct level, try the following solutions.
• User function 1.1.4 Window Frozen set to “Yes”:
Critical Parameter: Ask KROHNE for more advice before reconfiguring gauge.
This concentrates search for product level in a small defined zone and ignores interference
signals.The gauge will set up the “level window” on either side of the last reading with a plus/minus
range equal to half of the value given in Function 1.1.5. The gauge will then ignore all other pulse
reflections outside the “level window” as long as there is a reflection above the pre-set threshold. If
no pulse is detected, the instrument will change the Gain automatically as the pulse changes
amplitude.
• User function 1.1.4 Window Frozen set to “No”:
The instrument will search along the entire length of the probe. Warning : This may lead the
instrument to incorrectly identify a non-product reflection (e.g. a nearby beam or the nozzle) to be
the current level.
• Modification of User Function 1.5.1 Level Threshold:
Critical Parameter: Ask KROHNE for more advice before reconfiguring gauge.
The default threshold values do not normally need to be changed. However, the level threshold may
need to be modified if level is hard to detect due to parasite signals from obstructions in the tank
(nozzle, beams and mixers) or the measurement of products with very low dielectric constants.