G
Why vibration sensors output is adjusted for -10v for different sensitivity sensors also? why -10v is taken as reference? why -ve voltage only will be given to probe?
gsh,
There are vibrations sensors, and there are vibrations sensors. Specifically, there are velocity sensors (also referred to as seismic pick-ups). There are accelerometers. There are proximity probes.
This is a technical forum. <b>What kind of "vibration sensor" are you referring to? What company manufactures the "vibration sensor" you are referring to?</b> As this is a technical forum and you are posting a technical question, you should be providing as much information about the device or equipment you are asking about--technically speaking.
If someone approached you and said, "My watch isn't working. Can you tell me why?" and you couldn't see the watch, how would you respond?
With a series of questions to try to determine more about the type of watch (analog or digital), the type of mechanism (mechanical or electronic), and so on.
You have the ability to tell us what company manufactures the "vibration sensor" and what kind of "vibration sensor" you are referring to, which could help us provide a concise and timely reply.
I'm sure we all know that you are referring to Bently-Nevada proximity probes, and this question has been asked many times before on control.com. There is a 'Search' feature cleverly located at the top right corner of every control.com page which you can use to search the Archives of control.com for the answer to your question.
PLEASE, if you choose to post here in the future, provide as much information as you can about the part or equipment you are asking about. Remember, we can't see what you are looking at or dealing with. Even if you are working on an electric motor, is it an AC motor or DC motor? Does it have brushes or not? Is a squirrel cage induction motor or a wound rotor induction motor? Is it a series motor or a shunt motor? Is it double-ended or single-ended? You see, a motor is not just a motor. All motors do produce torque, but every motor is not like every other motor; many are very different depending on the application (pump; gantry crane drive; fan; elevator (lift); etc.).
Every vibration sensor is not like every other vibration sensor.
There are vibrations sensors, and there are vibrations sensors. Specifically, there are velocity sensors (also referred to as seismic pick-ups). There are accelerometers. There are proximity probes.
This is a technical forum. <b>What kind of "vibration sensor" are you referring to? What company manufactures the "vibration sensor" you are referring to?</b> As this is a technical forum and you are posting a technical question, you should be providing as much information about the device or equipment you are asking about--technically speaking.
If someone approached you and said, "My watch isn't working. Can you tell me why?" and you couldn't see the watch, how would you respond?
With a series of questions to try to determine more about the type of watch (analog or digital), the type of mechanism (mechanical or electronic), and so on.
You have the ability to tell us what company manufactures the "vibration sensor" and what kind of "vibration sensor" you are referring to, which could help us provide a concise and timely reply.
I'm sure we all know that you are referring to Bently-Nevada proximity probes, and this question has been asked many times before on control.com. There is a 'Search' feature cleverly located at the top right corner of every control.com page which you can use to search the Archives of control.com for the answer to your question.
PLEASE, if you choose to post here in the future, provide as much information as you can about the part or equipment you are asking about. Remember, we can't see what you are looking at or dealing with. Even if you are working on an electric motor, is it an AC motor or DC motor? Does it have brushes or not? Is a squirrel cage induction motor or a wound rotor induction motor? Is it a series motor or a shunt motor? Is it double-ended or single-ended? You see, a motor is not just a motor. All motors do produce torque, but every motor is not like every other motor; many are very different depending on the application (pump; gantry crane drive; fan; elevator (lift); etc.).
Every vibration sensor is not like every other vibration sensor.
G
gsh
sorry for the incomplete information
we are using in our plant Bently Nevada proximity sensors for turbine measurements such as key phasor, eccentricity, axial shift, etc. for key phasor probe sensitivity is around 7.87v/mm and axial shift probe sensitivity is around 3.94v/mm, but -10v dc output is taken reference for gap adjustment why? and why -ve voltage will consider for vibration probes.
we are using in our plant Bently Nevada proximity sensors for turbine measurements such as key phasor, eccentricity, axial shift, etc. for key phasor probe sensitivity is around 7.87v/mm and axial shift probe sensitivity is around 3.94v/mm, but -10v dc output is taken reference for gap adjustment why? and why -ve voltage will consider for vibration probes.
gsh,
Almost every instrument (with the exception of RTDs and thermocouples) has a "zero" setting, or needs to put in a linear range to operate correctly. That's what the -10 VDC does--puts the proximity probe and associated proximitor in it's linear range of output. (Some people believe the proper setting is -9.5 VDC. I don't know if Bently-Nevada (GE) publishes a specification for a particular proximity probes/proximitors.)
Come to think of it, different RTDs and thermocouples are usually used for different temperature ranges, probably because not every RTD or thermocouple is suitable for every range of use--so that's similar to "putting it in its linear range" I would imagine.
As for why the voltage is negative, that has been covered several times on control.com, and the 'Search' feature can be used to find the threads. (Reading the very short control.com 'Search' Help section is HIGHLY recommended before just typing a term or words in the 'Search' field....)
Almost every instrument (with the exception of RTDs and thermocouples) has a "zero" setting, or needs to put in a linear range to operate correctly. That's what the -10 VDC does--puts the proximity probe and associated proximitor in it's linear range of output. (Some people believe the proper setting is -9.5 VDC. I don't know if Bently-Nevada (GE) publishes a specification for a particular proximity probes/proximitors.)
Come to think of it, different RTDs and thermocouples are usually used for different temperature ranges, probably because not every RTD or thermocouple is suitable for every range of use--so that's similar to "putting it in its linear range" I would imagine.
As for why the voltage is negative, that has been covered several times on control.com, and the 'Search' feature can be used to find the threads. (Reading the very short control.com 'Search' Help section is HIGHLY recommended before just typing a term or words in the 'Search' field....)
G
GJA
gsh,
Given that accurate proximity probe measurements are critical for machinery condition monitoring and that gap voltage adjustment, prox probe or extension cable replacement may require extensive downtime, I verify linearity and displacement response using GE-VB's "wobbulator" or some other device.
It's important to understand that the probe, extension cable and proximeter comprise a matched system, clearly marked on the proximeter but often ignored. Use the wrong extension cable length, or use an 8mm proximeter with a 5mm probe, and the linear response will be way off. I test the complete set to avoid embarrassing mistakes.
The wobbulator's on-board micrometer allows you to measure the voltage output of the proximeter over a precise range of physical distances, or gaps, and the wobble-disk causes a voltage output over a range of displacements (0-10mils adjustable using the on-board dial indicator) in response to a variable speed rotating disk that's machined on a slope, thus simulating a rotating shaft that's moving toward and away from the probe at a precisely known distance and speed.
I usually find that a gap voltage of 9.5 is often in the center of best linear response for 5mm probes, which are typically used for measuring rotational displacement, or relative vibration. Some say "just set the gap voltage at ten volts" and forget about it, only to find they've used the wrong extension cable and end up having to pull a bearing cap to replace the cable, or worse.
Depending on the monitoring system, you can set the gap at a less than best linearity distance and enter the actual linear characteristics into the monitor, such as the GE-BV 3500 system. This is especially useful for differential expansion measurements on steam turbines where the accuracy of the "ramp" probe becomes very important.
You can have a machinist make a micrometer to test for linear response--which is reasonable assurance that it will pass the wobble displacement test--by making a clamp to hold the probe and a disk to fit over the end of a depth micrometer and a DC power supply to drive the proximiter. It's that simple. The disk material ideally should be made of the same material as the machine's shaft as the material does affect the linear response. If you've got the funding, I'd buy the wobbulator and get disks that match your shaft from GE-VB. It comes with a variety of clamping collars to fit most of their probes.
Given that accurate proximity probe measurements are critical for machinery condition monitoring and that gap voltage adjustment, prox probe or extension cable replacement may require extensive downtime, I verify linearity and displacement response using GE-VB's "wobbulator" or some other device.
It's important to understand that the probe, extension cable and proximeter comprise a matched system, clearly marked on the proximeter but often ignored. Use the wrong extension cable length, or use an 8mm proximeter with a 5mm probe, and the linear response will be way off. I test the complete set to avoid embarrassing mistakes.
The wobbulator's on-board micrometer allows you to measure the voltage output of the proximeter over a precise range of physical distances, or gaps, and the wobble-disk causes a voltage output over a range of displacements (0-10mils adjustable using the on-board dial indicator) in response to a variable speed rotating disk that's machined on a slope, thus simulating a rotating shaft that's moving toward and away from the probe at a precisely known distance and speed.
I usually find that a gap voltage of 9.5 is often in the center of best linear response for 5mm probes, which are typically used for measuring rotational displacement, or relative vibration. Some say "just set the gap voltage at ten volts" and forget about it, only to find they've used the wrong extension cable and end up having to pull a bearing cap to replace the cable, or worse.
Depending on the monitoring system, you can set the gap at a less than best linearity distance and enter the actual linear characteristics into the monitor, such as the GE-BV 3500 system. This is especially useful for differential expansion measurements on steam turbines where the accuracy of the "ramp" probe becomes very important.
You can have a machinist make a micrometer to test for linear response--which is reasonable assurance that it will pass the wobble displacement test--by making a clamp to hold the probe and a disk to fit over the end of a depth micrometer and a DC power supply to drive the proximiter. It's that simple. The disk material ideally should be made of the same material as the machine's shaft as the material does affect the linear response. If you've got the funding, I'd buy the wobbulator and get disks that match your shaft from GE-VB. It comes with a variety of clamping collars to fit most of their probes.
GJA,
Very good explanation and recommendations.
Would you please estimate how many bad new proximity probes, extension cables and proximitors you have discovered using the procedures you outlined? (Presuming the components were properly matched.)
Because, in my experience prior to B-N being purchased by a major multi-national corporation I never experienced a single failed new component, and I can only recall one failed extension cable since the purchase (and it was an intermittent connection in the connector).
Thanks!
Very good explanation and recommendations.
Would you please estimate how many bad new proximity probes, extension cables and proximitors you have discovered using the procedures you outlined? (Presuming the components were properly matched.)
Because, in my experience prior to B-N being purchased by a major multi-national corporation I never experienced a single failed new component, and I can only recall one failed extension cable since the purchase (and it was an intermittent connection in the connector).
Thanks!
