Page 12 of 20
█
© Brüel & Kjaer Vibro
● October 2017 ● C106635002 / V01
Technical alterations reserved!
EN
3.17 Over range
The VIBROCONTROL 850 Vibration Monitor is provided with an over range detection system.
The detection of an over range will not generate a system failure (OK failure).
The status of the alarm relays is active.
The DC analogue output will move to 20,5 mA to indicate the over range condition.
3.18 DC Analogue Output
At the “4-20 mA output wire” a DC output current will be available, which is direct proportional to the
vibration level. An output current of 4 mA at the DC output represents a value of 0 mm/s, while 20 mA
at the output represents full scale. Any value between 0 and full scale will then be positioned directly
linear between 4 mA and 20 mA at the analogue output.
Example 1: the vibration level is a known 60 mm/s with a full scale of 100 mm/s. The analogue output
should show:
𝐼𝐼
out
= 4 𝑚𝑚𝑚𝑚 +
𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉
𝐹𝐹𝐹𝐹𝑉𝑉𝑉𝑉𝐹𝐹𝑉𝑉𝐹𝐹𝑉𝑉𝑉𝑉
∗ (16 𝑚𝑚𝑚𝑚) = 4 𝑚𝑚𝑚𝑚 +
60
𝑚𝑚𝑚𝑚
𝑠𝑠
100
𝑚𝑚𝑚𝑚
𝑠𝑠
= 13,6 𝑚𝑚𝑚𝑚
Example 2: the analogue output shows 15 mA. The velocity is:
𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 = 𝐹𝐹𝐹𝐹𝑉𝑉𝑉𝑉𝐹𝐹𝑉𝑉𝐹𝐹𝑉𝑉𝑉𝑉 ∗ �
𝐼𝐼
out
− 4 𝑚𝑚𝑚𝑚
16𝑚𝑚𝑚𝑚 � = 100
𝑚𝑚𝑚𝑚
𝐹𝐹
∗ �
15 𝑚𝑚𝑚𝑚 − 4 𝑚𝑚𝑚𝑚
16 𝑚𝑚𝑚𝑚
� = 68,75 𝑚𝑚𝑚𝑚/𝐹𝐹
Please note that in order for the DC current output to function correctly it is necessary that the
DIP switches 3, 4 & 5 are in the “Off – Off – Off” position.
The impedance
load at the DC Analogue Output may NOT exceed 400 Ω.
3.19 Alarm Output (relays)
The VIBROCONTROL 850 is equipped with an Alert alarm relay, as well as a Danger alarm relay,
each having a break mode function upon activation (= FAIL SAFE). This means that these relays are
always in make mode, i.e. energized, while being in standby. This also means that the relays will be
“activated” in case of an interruption of the main power to the unit.
The relays are PhotoMOS Solid State relays. Excessive current and/or voltage will destroy the
relays. For this reason please do not apply any power source directly to the relay. Protect the
relay with a resistor in series that will limit the current or use as drive for a power contactor.