Technical Questions

Technical Questions



SCOUT / vbSeries: Are there any tasks I should carry out before performing a balance job?

Yes. We recommend you work through the following list of pre-balance procedures. These will help determine whether the high vibration levels are caused by imbalance or some other problem. They will also give you a benchmark for comparing your machine's vibration to industry standard acceptable levels.

  1. Before starting a balancing job to correct a reported vibration issue, begin your analysis by taking an overall vibration reading and comparing the results to the ISO 10816 specifications - Refer to the table below.
  2. Next, collect spectral data to ensure that you can verify a major contribution at 1X running speed. Also collect phase readings to reinforce that the high vibration is actually caused by imbalance. Phase measurements are key to determining if the vibration is caused by static or dynamic imbalance, and whether it can be addressed by the one-plane or two-plane method.
  3. As other faults might be present, correct any mechanical looseness that might create high 1X, 2X, or 7X vibration.
  4. Address any misalignment that creates high 1X, 2X, or 3X vibration. Also be sure to address any structural resonance at (or near) running speed that will cause unstable phase readings.

More about SCOUT / vbSeries. 

ISO 10816

This standard establishes the general conditions and procedures for the measurement and evaluation of vibration, using measurements made on the non-rotating parts of machines. The general evaluation criteria relate to both operational monitoring and acceptance testing and have been established primarily with regard to securing reliable long-term operation of machines.

The ISO standard defines four groups of machines according to their size and purpose. Machine operating conditions are separated into 4 coloured zones, which graphically demarcate acceptable and excessive vibration levels.

  • Green Zone A - Vibration values of a newly operational machine.
  • Yellow Zone B - The machine can run in continuous operation without restriction
  • Orange Zone C - The machine condition is unsuitable for continuous operation and should only operate for limited time periods. Take corrective measures at the earliest opportunity.
  • Red Zone D - The machine is experiencing dangerous levels of vibration which may cause damage.

SCOUT / vbSeries: How can I balance an overhung rotor?

Overhung rotors have characteristics such as Disk Skew and Gyroscopic Effects that can make them difficult or impossible to balance with standard single or dual plane balancing techniques. This FAQ describes two effective techniques for balancing an overhung rotor:

  • Technique for single plane balancing
  • Technique for dual plane balancing


The following method resolves static and couple imbalances separately. The static component is balanced first before dealing with any couple unbalance.

Step 1 - Static Balance

  1. Connect the channel 1 accelerometer to bearing B - Closest to the fan.
  2. Perform a single plane balance on plane C only - Closest to the bearings.

Step 2 - Couple Balance

  1. When the vibration level at bearing B is satisfactory, move the channel 1 accelerometer to bearing A - Furthest from the fan.
  2. If the vibration level of bearing A is not acceptable, perform a single plane balance on plane D using 'couple weights'. When placing a trial weight on plane D, also place an equal weight 180º opposite on plane C.
  3. When the instrument calculates the required balance weight, place it as directed on plane D and place an equal weight on plane C in a location 180º opposite. Use only the weight and location of the plane D weight when entering data into the instrument.

Step 3 - Final Static Balance

  1. When the vibration level at bearing A is satisfactory, move the channel 1 accelerometer to bearing B - Closest to the fan.
  2. If the vibration level of bearing B is not acceptable, perform another normal single plane balance in plane C - I.e. repeat step 1.


The following method combines the static and couple balance operations into one. This method can balance an overhung rotor in four runs (not counting trim balances). Essentially, you will need to perform a dual plane balance. However, when placing trial or trim weights on plane D, you will also need to place an equal weight on plane C in a location 180º opposite the weight positioned on plane D.

  1. Connect the two accelerometers on bearings A and B. Initiate a dual plane balance and collect the initial readings.
  2. For the 'left' trial weight, apply a known weight in plane C and take the left trial reading.
  3. If you have 'remove trial weights' selected, remove all trial weights.
  4. For the 'right' trial weight apply a known weight in plane D and an equal weight in plane C 180º opposite. Use only the weight and location of the plane D weight when entering data into the instrument. Take the 'right' trial reading and let the instrument perform balance calculations.
  5. If you have 'remove trial weights' selected, remove all trial weights.
  6. Balance the rotor by applying the weight in plane C as indicated by the instrument in the 'left' correction plane. For the 'right' correction plane, apply the weight in plane D as indicated by the instrument. You will also need to add an equal weight 180º opposite in plane C, i.e. for every balance and trim balance you will be applying two weights to plane C and one to plane D.

TIP: You can use the instrument's 'combine weights' function to combine the two weights in plane C into one - I.e. use one heavier weight instead of two individual weights.

The techniques outlined above are effective in reducing vibration on imbalanced rotors. If vibration persists this might be because the problem is not caused by imbalance. We advise you to check the machine to eliminate other probable causes of vibration before carrying out lengthy balancing procedures.  

How do I setup my PT878?

Please watch the below video with instructions on for setting up PT878: 


SCOUT / vbSeries: How often should I have my SCOUT / vbSeries instrument and its accelerometers calibrated and how do I go about it?

SCOUT / vbSeries instruments have very stable hardware and firmware. However, we recommend yearly performance checks for the instruments and a full calibration during the final year of warranty. This verification check is not covered under your warranty and is a chargeable service. However, in the unlikely event that re-calibration is required, and the standard warranty conditions are met, the cost of the re-calibration will be covered under warranty.

Depending on your business processes, you might need to run performance checks at more regular intervals. These checks can be performed by an appropriate service near you.

In practice, the requirements of your customers or your certification board will typically specify a more frequent verification of the calibration.

We strongly recommend checking the calibration of any damaged instrument before taking further measurements. If a calibration problem is suspected, the instrument must be sent to our site for calibration, complete the RMA form. Re-calibration can only by performed by certified GE professionals.

How to find a Technical Support Contact?

In the main website menu click Contacts Us >> select I need Support or Service for my GE product >> click Service Directory.

The Tech Support contact information for each M&C product line could be found there.

I cannot access the Calibration menu on my DPI 610/615 using the Calibration PIN 4321. Is there an over-ride / by-pass PIN?

To over-ride an unknown PIN use the PIN 6100 followed immediately by pressing the SETUP key (not the ENTER key).

I cannot access the Calibration menu using the PIN 000. Is there a way to over-ride the PIN number?

First check that the CAL enable link (LK1) located on the rear of the PCB is fitted in the checked position. If the link is not in the checked position then move the link to the checked position and re-enter the pin 000. If you still cannot access the Calibration menu then the Cal pin will require resetting as follows:

Press the SET key until the display shows PIN, press the F2 key to access the pin menu, enter the pin number 212, next enter the new pin as 000, then re-enter 000 to confirm the new pin number.

The Calibration menu can now be accessed using the pin number 000. For further information on changing the pin number refer to the DPI 740 User Manual K200.

I cannot gain access to the calibration menu using the calibration PIN 4321. What should I do?

First check that the calibration enable link is fitted in the ticked position. The link is located on the display side of the PCB. If the link is fitted in the ticked position and the PIN number 4321 still does not gain access to the calibration menu then enter the number 7050 followed by pressing the UNITS key.

SCOUT / vbSeries: What is the accuracy of the low frequency (slow speed) response of the SCOUT / vbSeries instrument?

There are three limiting factors to the low frequency response of your system:

  • The response of the sensor(s) being used - See more comments near the end of this page.
  • The effect of the AC decoupling capacitors in the instrument (does not apply when using DC coupling).
  • The integration process from acceleration to velocity (& displacement), which must remove low frequency components to avoid output drift.


We specify the SCOUT / vbSeries portable instrument and vbOnline system frequency response down to 1 Hz (60 cpm). You can take readings below this frequency but the instrument's sensitivity drops off rapidly because this region includes the corner frequencies of the AC decoupling filter and the integrators.

NOTE: The tables provide an indication of the nominal response, not a calibration.


For the best low frequency response you must bypass the AC decoupling filter and use DC coupling. We provide this capability in the vbOnline system and in selected SCOUT / vbSeries portables. To measure ICP® accelerometers using DC coupling:

  1. Set the sensor's Voltage Range and Coupling to DC (0 V to 20 V).
  2. Keep the Drive Current enabled.

When measuring acceleration this gives you a FLAT (100%) response down to 0 Hz DC. The trade-off is that there is more low-frequency noise, so more ski-slope in the spectra.

For measurements of velocity or displacement the response is not 100%, there is still significant low frequency attenuation. This is because the integration process from acceleration must remove the DC offset and low frequencies, to avoid output drift. The response is better than that indicated in the AC table above, typically halfway between the values given and 100%.

However for vbOnline firmware versions from v5.81 we have introduced a special low-frequency integration mode. This yields the velocity and displacement responses given in the table below.

Low-frequency integration mode is enabled and used by applying the following settings:

  • Sensor Coupling = DC
  • Fmax = 100 Hz (6000 CPM)
  • Fmin = 0
  • Sensor settling time = 20 ... 30 s
  • Sensor Sensitivity = 500 mV/g or higher


The best low frequency response is obtained with Fmax=100Hz. However, all Fmaxes up to 500Hz do use this mode, with responses scaled to maintain the -3dB point at 0.2% of Fmax.

High sensitivity sensors should be used because low-frequency vibration (under 1Hz) has extremely low acceleration levels - system noise may dominate the signal.



All Commtest instruments support sensor bias checks for AC sensors (i.e. ICP accelerometers). However that automatic checking is not available for DC coupled sensors. Instead you can take Average Value measurements from the sensor and set Average Value alarms to check that the acceleration offset is as expected for the typical 12V bias:

  • 100 mV/g expect 120 g offset Suggest alarms if outside 80 .. 160 g
  • 500 mV/g expect 24 g offset Suggest alarms if outside 16 .. 32 g



vbClassic (vb1000, vb2000, vb3000) instruments prior to serial number 11500 (running firmware versions 3.xx and earlier) used an earlier version of analog input circuit. For these instruments the best low frequency accuracy is obtained by taking velocity or displacement readings, which gives a response similar to the AC coupled table above. We do not recommend the use of acceleration on these instruments below 10 Hz.



Accelerometers are typically specified as having a ± 3 dB response (e.g. between 0.5 Hz and 15 kHz). Their response usually drops off towards -3 dB at the lower frequency limit so you will need to take this into account if you want to calculate the most accurate system response. Ideally you should consult the frequency response curve published by the sensor manufacturer. However, we provide the table below as an indication of the likely response based purely on the Low Frequency Limit (LFL, e.g. 0.5 Hz or 30 cpm).


If you are analyzing a bearing for faults, bearing tones will be at higher frequencies than the running speed, so will be less affected by the low frequency response.

Demodulation is particularly useful for detecting bearing faults on slow speed machines. The signal is derived from high frequency impacts and the Demod/decimation process does not attenuate low frequencies, so Demod has a flat (100%) response.

On slow speed machines, you can use Demod time waveform measurements to look at the time differences between impact events in the time record and compare these with fault frequencies. This is only available on vbX instruments running v3.0 firmware or later.

For more detailed information you can purchase the technical paper 'Low Speed Machines' from Technical Associates of Charlotte, P.C.


It is possible to balance very slow speed machines using the vbSeries instruments (e.g. 30 RPM) even though the reading may have a reduced response. This is because all balance runs are made at the same speed and the balancing algorithm analyses the effect of fitting the trial weight. A low sensitivity at the running speed will affect all the Initial, Trial, and Balance runs to the same extent, so is effectively self-compensating.

What to do if the PT878 goes into a rebooting loop and will not turn on?

This condition is a result of the battery power being too low such that it corrupts the bootup file. In order to fix this problem, you must take the following 2 actions: 

1. Reset the meter.

2. Recharge the battery for 6-8 hours prior to using.

In order to reset the meter:

1. Turn the meter on. 

2. When 'Program CRC' appears on the screen press and hold the “0” key for about 10 sec. 

3. The following should appear: “Reload Flash via Infrared (Yes/No)?”. Press No (F2). 

4. The following should appear: “Erase all Sites (Yes/No)?” Press Yes (F1). 

Upon resetting the meter, the units will switch to metric. If this is the desired selection, reprogram meter as necessary, otherwise you will need to reset to English units. To do this, select Menu --> Meter --> Units --> Select English. If the condition does not clear after resetting and recharging the meter, the battery will need to be replaced. You can either order a new battery (part number 200--081) through Customer Care, or send the meter in for repair.