1. Orange box input

2. Input couplings Overview ICP Accelerometer
Displacement sensor (negative supply)
Positive power supply sensor
Bipolar sensor
Grounding
Most vibration sensors require a power supply, however some sensors (Like the CCLD ICP sensors require a current supply)
Other require a negative supply voltage (proximitor probes)
Most other powered transducers require a positive power supply
Some sensors does not require power supply they are called bipolar since the output is both positive and negative.
Name. Etc.

3. The Orange box input: Multi purpose Every channel floating
Internal Ref voltages
PWR+
+14 V
4 mA V Hi
~10 M Ω
0 V
500 Ω LO V
~10 M Ω
PWR- (COM)
-14 V
The input is made for either positive or negative power supply, as well as current supply
, the Hig impedance feedaback resistors make it possible to also connect bipolar transducers.
Each input is totally floating and has its own power supply.
By opening the ICP switch a constant current generator is generating the current required for an ICP transducer.
If the ICP switch is open a voltage limitor is coupled in (Here illustrated as Voltage source) This will make sure that the supply current is always 12 V.
This is not true if the transducer is consuming less than 4mA where the 4mA current supply will take over, however all transducer supplies are consuming more than 4 mA so this is in general not a problem. The Hi and LO inputs are floating, but a very high impedance resistors will pull them to the center voltage of the input stage, which makes it possible to measure bipolar voltages.
GND

4. Integrated Circuit Piezoelectric (ICP) Accelerometer Constant Current Line Drive (CCLD)
Using a constant curent

5. ICP Accelerometer - Constant Current Line Drive (CCLD)
PWR+
4 mA V HI
~10 M Ω
0 V
500 Ω V LO
~10 M Ω
-14 V
The ICP accelerometer is a piezoelectric accelerometer with a built in preamplifier which is driven by a constant current.
The built in preamplifier is equivalent to a variable resistor, where the resistance to the current is propotional to the instant acceleration of the transducer.
The CCLD (Constant Current Line Drive is fed by a 4 mA current source.
The input stage itself cannot consume the power used to drive the transducer preamplifier therefore both the positive and the negative power supply (COM) is connected.
PWR- (COM)
GND
Cable shield only if not connected at machine

6. VibraSens ICP Accelerometer Cable Colour Coding
Cable connectors 1 2
VibraSens 109 with
Connector M12
Shield: Green
HI: Pin 4 Black
LO: Pin3 Blue 4 3 HI LO
Remember cable pin numbers are mirrored

7. Hansfort ICP Accelerometer

8. Proximity probe – Displacement Sensor – Eddy current probe
COM
Measurement
Supply
Voltage
(-24 V)
Out (Sig)
VT (-DC)
3 wire
This is what a BN person sais about the reason for the choise of negative supply voltage in the vibration industry.
(Note that some acceleration preamplifiers such as the B&KV 2636 also uses -24V supply voltage)
When Don Bently worked on making solid-state versions of the eddy-current measurement system (it was actually originally designed in the 1930s by GE engineers using vacuum tubes), he had a choice between using N-P-N transistors or P-N-P transistors. At the time, transistors were quite expensive, so he chose the least expensive of the two: P-N-P (apparently, PNP transistors they were less expensive to manufacture 50 years ago than their NPN counterparts). Because the circuits used PNP transistors, a negative bias voltage was required rather than a positive bias voltage. Don chose -18V. This was later changed to -24V to allow more linear range from the transducer. At that time, the industrial instrumentation community had not yet standardized on +24 vdc, and by the time they did, there were so many Bently Nevada eddy current vibration sensors installed that changing to +24V rather than -24V was not greeting with enthusiasm by users. Hence, it has remained -24V to this day.
Applications: Orbit, Shaft Centerline Vibration, Tacho

9. Displacement Sensor (Negative power supply)
500 Ω
+12V
~10 M Ω
PWR+ Hi LO
GND
VT (-DC)
Out (Sig)
COM
4 mA
PWR- (COM)
+14 V
Every manufacturer has their own nomination for the 3 wire system.
Brüel & Kjær Vibro has a 4 wire system where they connect 0 V and the Signal Com internally to the COM at the oscilaltor demodulator.
General Electric (Bently Nevada) uses the terms Com, Out and VT While B&KV uses COM, Sig and -DC

10. Transducer with positive power supply
500 Ω
+12V
~10 M Ω
PWR+ Hi LO
GND
VT (+DC)
Out (Sig)
COM
4 mA
PWR- (COM)
Most standard transducer in the process industry (except for the proximitor probe displacement sensors) have a positive power supply as standard

11. Current measurement (4mA – 20 mA)
Do not connect
PWR+
+12V V
+14 V
PWR+
4 mA V
~10 M Ω Hi
0 V
500 Ω V LO
4mA-20mA
Signal
~10 M Ω
-14 V
Many control systems deliver a 4-20 mA current which is propotrtionaln to some signal. (The Offset and linear scaling has to be specified in each case)
Do not connect PWR, this will introduce a 4mA offset
PWR- may be connected to low for offseting the signal.
PWR- (COM)
GND

12. Velocity probe

13. Bi – Polar (Velocity Probe, Signal Generator or Buffered Out)
PWR+
4 mA V Hi
~10 M Ω
0 V
500 Ω V LO
~10 M Ω
-14 V
The High Impedance feedback resistors will make sure that
PWR- (COM)
GND

14. Grounding Grounding is used for Protective grounding
Avoiding power shock accidents.
Removing of low frequency ”hum”
50 Hz noise
In some countries 60 Hz
Ground loops
Removing high frequency noise
Introduced into the power network by variable speed motors etc.
Transmitter and radio noise
Anchoring a floating system
”Floating systems” have a tendecny to float on AC voltage corresponding to half the power supply
Due to high frequency filter
Connect the shield to ground only if
The shield is not part of the signal path,
The shield is not used for power supply
The cable shield is grounded at the transducer position

15. Ground loops
Sensor
Coax Cable
Monitor S G E I ~

16. Traditional ground loop (low frequency) avoidance
Monitor
Sensor
Twisted Pair ~
Screen Isolated
(Ground Loop
not Established)
Sensor Element Isolated ~ EG

17. Hig frequency filters on input may give half the suply voltage
High frequency filter +
230 V AC
115 V AC if not grounded -