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Being able to determine an oil’s solid particle concentration (number and size of contamination particles in a defined volume) is one important feature in a well-defined fluid monitoring program. Armed with particle count information, an operator is able to make several assumptions about the condition of a hydraulic or lubrication system.
The operator can postulate about filter efficiency and configuration, a component’s adherence to required cleanliness levels, changes in the system’s wear and attrition rates, and changes of secondary contamination affecting the system, such as damaged cylinder seals. Such information allows the operator to make adjustments to the system and fluid environment that will ensure optimal machine performance.
There are different ways to count particles in fluids. One way is to extract bottle samples from the system and examine the samples in a laboratory. Another way is to periodically take online particle counts during machine operation. It is also possible to install dedicated onboard particle counting sensors for real time analysis. All three methods for monitoring systems have advantages as well as disadvantages.
Advantages of Bottle Sampling
Ability to eliminate conditions that may cause error in the use of automatic optical particle counting, for example, interferences from air or water.
Fluids with high viscosity or extreme contamination can be conveniently diluted prior to counting.
A laboratory offers further analytical possibilities, such as advanced quantitative examination of the contamination or wear debris present.
Disadvantages of Bottle Sampling
Elapsed time between sampling and analysis.
Possible erroneous readings of the sample cleanliness due to either contamination introduced during extraction or unclean sample bottles.
Difficult to interpret dynamic changes in the system.
Advantages of Online Particle Counting
Ability to take measurements at multiple points on the system during operation (although the same can be said for bottle samples).
Most outside influences such as extraneous contamination can be eliminated.
Results can be checked against required cleanliness levels immediately.
Statistical repeatability and reproducibility of the results can be ensured by the increased number of sequential tests.
Dynamic changes in the system can be measured and used for diagnostic purposes.
Flushing procedures can be monitored to determine when the required cleanliness levels have been achieved.
Time intervals can be optimized.
Permanent online counting makes it possible to monitor critical systems. For example, a turbine bearing’s lubrication oil cleanliness can be observed via the Internet or intranet.
Disadvantages of Online Particle Counting
Internormen-Filter GmbH’s contamination control system, CCS 2, is an optical online particle counter that can be used in mobile or stationary applications in systems with high-pressure or high-viscosity ranges. The counting is performed in eight different counting channels at >4 µm, >4.6 µm, >6 µm, >6.4 µm, >10 µm, >14 µm, >21 µm and >37 µm. These channels are set using a calibration file. The required test volume is 10 mL. The results can be reported in either the number of particles per mL or 10 mL. They can also be reported in accordance with the ISO 4406:99, ISO 4406:87 or NAS 1638 standards.
The fluid is fed by a small test port, such as a minimess. While performing a count, a cylinder fills up and the oil from the cylinder is forced past a laser sensor by an electric-driven piston. This method ensures that the volume of oil flowing past the sensor remains constant.
Because the CCS 2 is adaptable to various testing methods, operating procedures can be customized to focus on particular applications. This feature can play a big role in increasing the operator’s efficiency. Every CCS 2 testing method includes automatic flushing procedures. In addition, it is not necessary to set pressure or volume flow.
The following test methods can be performed using the CCS 2:
Measurements are taken automatically every 20 seconds. The results of the past 100 measurements can be displayed and saved in a diagram using common standards. This feature automatically collects and stores dynamic data for purification procedures or for roll-off cleanliness monitoring.
After starting the program, a flushing procedure and three consecutive counts are initiated. The numbers of particles from these three measurements are averaged. The display can show either the number of particles for a separate channel or the particulate level based on ISO 4406:99 or NAS 1638 standards. The results can be printed or they can be saved in the particle counter’s memory, where the CCS 2’s software can manage the stored data. This method of measuring is especially useful for routine solid particle contaminant monitoring of systems where there are pre-set limits for the cleanliness level.
The program performs automatic measurement after certain periods of time. The setup menu can be used to set the number of measurements to be taken and the interval at which they will be taken. Every measurement includes one flushing cycle and three separate tests. Results are reported as the arithmetic mean. A certain particulate level based on ISO 4406:99 or NAS 1638 can be programmed as a limit.
Measurements outside the limits are indicated on the display and the measurements also can be sent to an output interface on the CCS 2. Analysis results are saved automatically. They are shown on the display and can be printed. This method of measuring is useful for automated continuous monitoring of a hydraulic fluid. It ensures low-fluid extraction over time.
(Optional Measuring Method)
The sample is introduced to the CCS 2 using an external apparatus (the BSS 2), which can also be used to free samples from gas using a vacuum system (Figure 1).
Figure 1. Contamination Control System CCS 2
A special bottle sampling software included in the CCS 2 makes the interaction of the two devices easy and accurate. Measurements and documentation are laboratory quality. In addition, it can be used to run calibration fluids based on ISO 11171.
(Optional Measuring Method)
The CCS 2 can be integrated into local networks or the Internet, allowing for remote access and operation. Measurements using the CCS 2 can be initiated from a Web-site provided by Internormen. Results are also displayed on Internormen’s Web page. This method allows for permanent online fluid monitoring. It is useful for monitoring sensible machinery components or hard to access systems, even in offshore areas.
The CCS 2 has access to four separate data memory blocks, each holding up to 100 measurements. Saved values can be reported either as the number of particles for each measurement or as the particulate level based on ISO 4406:99, ISO 4406:87 or NAS 1638. The internal RS 232 and the data-management software make it possible to transfer the data to a PC and manage it using Microsoft Excel (Figure 2).
Figure 2. CCS 2 Data Manager.
Counted particles during the cleaning process
of a hydraulic unit with a 5µm(c)-filter.
The CCS 2 must be sent offsite for the certified secondary calibration based on ISO 11171. However, calibration based on ISO 11171 can be performed by the user with the help of a BSS 2 or the optional software for automatic calibration using a special solution for secondary calibration.
Figure 3. Degassing of an Oil Sample Using BSS 2.