Vibration monitoring is a crucial component for almost any manufacturing concern, especially when facility managers are charged with ensuring the performance of high power, not to mention high cost, equipment. With that in mind, Metrix has been committed to stressing the importance of vibration monitoring and providing tools at an affordable price. For over twenty years, we have been ISO-9001 certified, offering reliable equipment for the multiple industries. Below, we draw upon that experience to answer some common proximity device questions our DPS 1.35 customers have shared and our take on best practices you can follow.

WHAT IS CROSS TALK, WHEN DO YOU HAVE TO WORRY ABOUT IT, AND HOW DO YOU ELIMINATE IT?

Cross talk elimination is used when proximity probes are close together, typically less than 1 inch. This DPS 1.35 feature is used on one of the probes that could interfere electrically with another probe close by. This feature can be used on an MX2033 Driver or MX2034 transmitter proximity probe system. This feature shifts the oscillation frequency of the DPS unit so it is different from the adjacent probe, thereby, preventing cross talk interference. Do not use this feature on both probes that are close by, if you do you will continue to have a cross talk problem albeit at a different frequency. Only use cross talk elimination on one of the probes of the set.

For example, if you request cross talk elimination on one of the two adjacent DPS units is a Metrix DPS system, the pair you receive from our manufacture will have labels “X” and “Y” respectively. The standard DPS unit has no label for cross talk and it is default to “X”. However, if you experience cross talk in your application, you can convert one of the two adjacent DPS units to “Y” configuration in the field. Specifically, our technicians have provided this option through the advanced settings in the Metrix DPS configuration and utility software. 

In close proximity probe applications, the Metrix DPS can be calibrated with a different driving frequency that allows the probes to be within 0.5 inches of each other and not interfere with each other probe’s signal. This is perfect for the air machine market, due to the small (1-inch) shafts typical of these machines. Competitor probes have to be at least 1.5 inches apart to measure properly. 

WHAT IS THE INVERT BUFFERED OUTPUT POLARITY USED FOR?

Using the DPS 1.35 some customers want a positive output from the BNC of the MX2034 transmitter. Normal polarity is negative for output at the BNC of the MX2034 transmitter, this feature allows the user to change the output polarity to positive. This feature is only applicable to the MX2034 transmitter.

As with before, this feature is accessible through the advanced settings in the Metrix DPS configuration and utility software. 

WHEN WOULD ONE ENABLE SPIKE SUPPRESSION?

Using a MX2034 transmitter, this DPS 1.35 feature is used to inhibit high amplitude electrical noise from outside the vibration monitoring system from impacting the performance of the vibration transmitter system. This feature temporarily suppresses high amplitude, short duration, typically less than 50 millisecond vibration spikes, like those induced possibly by a portable radio when keying the mic.

If this feature is selected, any vibration spike greater than the full-scale range (default), or lesser value selected by the user, will be suppressed for the default duration of 1 millisecond or the time duration selected by the user up to 1000 milliseconds (1 second). During a spike suppression event, the output of the vibration transmitter will go to 3.0mA for approximately 0.25 seconds to inform the control system that a spike suppression event has occurred. 

Vibration amplitudes greater than the spike suppression setting, that last longer than the Spike duration setting, will be reported normally via the 4-20 mA output. The dynamic output via the BNC, on the transmitter, is not impacted by enabling spike suppression.

HOW DO YOU CHANGE THE UNITS TO METRIC FOR VERIFICATION AND REPORTS?

This is a common question asked by our customers, and the answer is simple. Go to the “Advanced Settings” tab and select “Metric,” the units for the table and plots on the “Verification” tab are now in metric units. However, this does not change the configuration of the transducer, which can be changed on the “Home” tab. This feature works for both the MX2033 Driver and MX2034 transmitter.

WHAT DOES THRUST DIRECTION UPSCALE MEAN?

For the DPS MX2034 transmitter the “Upscale” selection will correlate the low value of the full-scale range with the 4mA output of the transmitter, and the 20mA output at the high value of the full-scale range. The “Downscale” selection will correlate the high value of the full-scale range with the 4mA output of the transmitter, and the 20mA output at the low value of the full-scale range. This can be useful for the operator, the control system or display device. This feature can be accessible through the 

WHAT IS THRESHOLD AND HYSTERESIS USED FOR WHEN USING THE MX2034 AS A SPEED TRANSMITTER?

This DPS 1.35 feature for the MX2034 transmitter is used to improve the performance of the speed measuring system. The “Auto” setting allows one to use an auto threshold setting, which will trigger the DPS with a large negative pulse (greater than -6Vdc), whereas the manual threshold setting allows the user to select the threshold value (usually -13 Vdc or greater) and a hysteresis band of up to +/- 2.5 Vdc for a negative going pulse. One must ensure the negative-going pulse will produce a more negative voltage than the hysteresis dead band. Hysteresis creates a dead band around the threshold value.

For example, assume the initial gap voltage is set to -10 Vdc, if the threshold was set at -13 Vdc, and the hysteresis was set at +/- 1.0 Vdc, the negative going pulse would have to pass -14 Vdc (-14Vdc = -13Vdc -1Vdc) to have counter within the transmitter see the pulse, and then the counter would not reset until it saw the voltage pass through -12 Vdc (12Vdc = -13Vdc + 1Vdc) on its way back to the original gap voltage. Also note that if the initial gap is set to -10 Vdc, and the threshold is manually set to less than -10 Vdc the system will not work because the negative going pulse is always exceeded. This gets extended to the hysteresis dead band: it must always be more negative than the initial gap voltage (for example, if -10 Vdc is gap voltage, then dead band of -12 Vdc to -14 Vdc is okay). Using threshold and hysteresis are great ways to help reduce noise and increase accuracy in a speed measurement system.

HOW DOES ONE CHANGE THE TARGET MATERIAL FOR DPS 1.35?

Using Metrix DPS configuration and utility software, the “Change Configuration” menu option on the “Home” page tab allows one to change the target material from AISI 4140 Carbon Steel to another shaft material. Only Metrix Probe Series MX8030 and MX2030 allows the user to change to the other available materials listed. The materials listed represented 95 percent of the material types ever ordered from Metrix. All other probe types only have AISI 4140 as the target material in our standard delivery. However, if you have special target material other than AISI 4140 and request a probe series other than MX8030 and MX2030, you can contact Metrix directly for assistance.

HOW DOES DPS 1.35 HANDLE UNKNOWN TARGET MATERIALS?

While connected to a DPS Unit, using Metrix DPS configuration and utility software, the “Unknown Material Calibration” tab functions allow the DPS Proximity Probe System be calibrated to an unknown target material using this process:

  1. Take advantage of the Metrix 9060-SCDM (shaft calibrator dial micrometer) or the 9060-SCTS (shaft calibrator touch select) to calibrate the Metrix DPS with the unknown shaft material.
  2. These systems allow one to take data directly on the shaft target material.
  3. Unknown target materials result in a trial-and-error process. For the first iteration, use AISI 4140 Carbon Steel material type. If the verification check is running cold, then a custom calibration should be effective. If the verification is running hot, and exceeds 19Vdc, try a less dense material like one of the stainless steels.

HOW ARE CHANGES IN SYSTEM LENGTH ALLOWED FOR DPS 1.35 PROXIMITY PROBE SYSTEMS?

The “Change Configuration” menu option on the “Home” page tab allows one to change the system length of a DPS. This DPS 1.35 feature allows the user to switch between standard system lengths for the Probe Series selected:

The Metrix 7200 and BN 3300XL has 15 to 30 feet system lengths listed only. The 3000 Series probes only have 15 and 20 feet listed.

The Metrix MX8030 and MX2030 Probe Series allow the DPS to take advantage of extended systems lengths from 3 to 40 feet for vibration and thrust, and up to 65 feet for speed measurements. If a user wants to use a length other than listed, like 25 feet, the user would use either a higher or lower system length and perform a verification check to determine which length provided the best results. If the verification is not within limits a custom calibration can be conducted using the verification voltage values.

Users can use the Metrix MX8020-001 cable trimming and connector kit to alter the length of a MX8030 probe or MX8031 extension cable. Users no longer have to keep coils of extension cable in their junction boxes.

HOW DOES ONE CHANGE THE FULL SCALE RANGE FOR THE DPS 1.35?

The “Change Configuration” menu option on the “Home” page tab allows one to change the MX2034 transmitter full scale range. This feature is dependent upon what is selected for the MX2034 transmitter measurement. The MX2033 driver output goes to a monitoring system, so the full scale range is not used. 

If the transmitter measurement is for position, then the 4 to 20mA scale can be selected for the appropriate displacement output, either in mils or microns. If the transmitter measurement is set for vibration, then the 4 to 20mA scale can be selected for the appropriate vibration output, either in mils peak to peak or microns peak to peak. Finally, if the transmitter measurement is for speed, then the 4 to 20mA scale can be selected for the appropriate speed output in revolutions per minute.

A LOOK AHEAD

Next month, in the concluding half of this article, we’ll address even more common questions customers have brought to use on getting the most out of their proximity devices. From verification reports to custom calibration to comparison against an analog driver or transmitter, there’s still a great deal to learn.  

FOR MORE INFORMATION

Metrix pioneered the concept of simple, affordable machinery protection with its mechanical vibration switch offerings, revolutionary 4-20mA vibration transmitters, robust high-temperature velocity sensors, and innovative impact transmitter technology for reciprocating machinery. Metrix has been ISO-9001 certified for more than two decades and is committed to quality and continuous improvement of its manufacturing processes. For more information, visit www.metrixvibration.com.

MODERN PUMPING TODAY, August 2022
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