KLEEV USA’s – Top Mount Level Switches

KLEEV USA’s top mounted displacer and float level switches are the perfect solution when limitations prevent you from putting another chamber on the process vessel. KLEEV USA offers a full line of vertical top mounted level switches that are individually built to your exact specifications. Not only will they meet your needs, they will provide a long life of dependable service.



Versatile workhorse
Clean and simple device
Float and displacer models
NPT or flanged models
User adjustable set points on displacer units
Special calibration available from factory
Manual check mechanism option for displacer models

Engineered to your order
Variety of models, materials and connections to choose from
Wide range of pressure and temperature ratings
Infinite set points in one-, two- or three-stage models
Every KLEEV USA’a top mounted level switch can be custom made to your exact specifications – talk to a factory Sales Engineer or your local Representative

Product support
Sales Engineers are available to answer your questions and help you select the level switch that best fits your application

Simple to use
Easy to install

Solar PV Array Cleaning Guidelines



Dirt built-up over the solar arrays can substantially affect system performance. It is essential to clean the modules regularly to maximize energy output from a solar power plant. However, wrong cleaning practices, bad quality water and use of inappropriate cleaning agent may damage modules and other array components and lower system performance as well. It is also essential to train the cleaning personnel on proper cleaning methods and use of appropriate cleaning tools.

In this article, we are discussing few recommendations for cleaning solar modules in general. Specific cleaning procedures will be based on module manufacturer’s instructions, site condition, quality of water and cleaning mechanism used.

(i) Safety of personnel: Solar modules are connected in series and it generates upto 800V DC. Cracks in modules or damaged cable or joints in a string are extremely dangerous for cleaning person particularly when the modules are wet. Even during low level of sunlight the array will generate lethal voltage and current. Therefore, it is important to inspect modules thoroughly for cracks, damage, and loose connections before cleaning. Cleaning personnel shall wear appropriate electrically insulating Personal Protective Equipment (PPE) during cleaning.

(ii) Cleaning time: The recommended time for cleaning modules is during low light conditions when production is lowest. The best time to clean modules is from dusk to dawn when the plant is not in operation and risk of electrical shock hazard is minimum.

(iii) Quality of water: De-ionized water should be used to clean the modules. If de-ionized water is not available, rainwater or tap water can be used. Tap water must be of low mineral content with total hardness less than 75ppm. In case mineral content of water used is more than 75ppm but less than 200ppm the water must be squeezed off to prevent scale build up over module surface. Water with mineral content of more than 200ppm should NOT be used. Water must be free from grit and physical contaminants that could damage the panel surface.

(iv) Use of cleaning agent: A mild, non-abrasive, non-caustic detergent with deionized water may be used. Abrasive cleaners or de-greasers should not be used. Acid or alkali detergent must not be used.

(v) Removing stubborn marks: To remove stubborn dirt such as birds dropping, dead insects, tar etc., use a soft sponge, micro-fiber cloth or non-abrasive brush. Rinse the module immediately with plenty of water.

(vi) Drying: Modules should be dried after rinsing using a chamois or rubber wiper with a plastic frame on an extension pole. Wipe the module surface from top to bottom to remove any residual water from the module.

(vii) Water pressure: Water pressure should not exceed 35 bar at the nozzle. Use of high pressure hoses for cleaning may exert excess pressure and damage the modules.

(viii) Water temperature: Temperature of water used for cleaning should be same as ambient temperature at the time of cleaning. Cleaning should be carried out when the modules are cool to avoid thermal shock which can potentially cause cracks on the modules.

Why calibrate temperature sensors?

Temperature sensors are used in applications ranging from mobile phones to food refrigeration. But where quality measurements are critical, their calibration is essential, writes David Southworth, sales & marketing manager at Isothermal Technology, a company with 30 years of experience in temperature calibration.

The requirement to measure temperature is enormous. Pause to think of the devices around us. In many cases there is an obvious need to measure temperature – from the central heating control to the refrigerator, the kitchen oven to the heating system in the car. Perhaps you have a thermometer in a greenhouse or a desktop weather station? And mobile phones and laptops all have temperature sensors. Are you sitting on a chair? Well the materials from the plastic cover to the steel legs are processed at particular temperatures to ensure the quality and to avoid wasting energy. Sipping a cup of coffee? The milk in it will have been pasteurised at a particular temperature. In fact, temperature sensors surround us in our daily lives.

In many areas the temperature is not critical. If, for example, the display in the car reports 19°C but in reality the temperature is 21°C, life goes on. No great trust is required and the error may never be noticed. But in other areas, good quality measurements may be critical. Consider, for example, the cost and long term business damage if a supplier of refrigerated food discovered the goods had not been transported within agreed limits.

In power generation, being able to make accurate measurements can save energy, and energy savings brought about by even a small improvement in measurement might save hundreds of thousands of pounds a year. In a medical setting, be it a thermometer being used for diagnosis or a sensor controlling an MRI scanner, poor measurements could have disastrous consequences. So, whilst some sensors may never be calibrated, others may need calibration to ensure quality, make cost savings from increased efficiency, or even to safeguard human life.

How to calibrate

A complete measuring system will compromise both a sensor and a measuring instrument. Instruments can be calibrated by disconnecting the sensor and connecting a temperature simulator – for example, a thermocouple can be replaced with a voltage source that injects voltages equivalent to the thermocouple signal over a range of temperatures.

The problem with this approach is that it only checks the instrument, not the sensor. In many cases sensors undergo wide changes in operating temperature and can be used in hostile conditions. As a result the sensor can drift significantly, and potentially more than the measuring device, which may benefit from both modern electronic technology and being located away from extremes of temperature.

To calibrate the whole measuring loop a portable heat source can be used in situ. Now, the sensor can be placed into a heat source and temperature cycled so that the whole loop, sensor and instrument can be verified.

Portable and transportable heat sources are now available to cover the range from -100°C to 1300°C. Isothermal Technology (Isotech) can, for example, provide small handheld sources through to large devices capable of accommodating large sensors.

Types of heat sources

For on-site calibration Dry Block calibrators are usually the most convenient. Here, a metal block is heated or cooled to the required temperature and the sensor or sensors to be tested are placed into the block. There are also multi-function calibrators that can be used both as a Dry Block and also Stirred Liquid Baths. With this type of device the thermometers are placed into a suitable liquid, usually silicon oil, rather than a drilled metal block.

Some Dry Blocks are used in a way that the sensor being tested is compared to the displayed temperature value. For greater confidence in measurements a separate higher accuracy thermometer is placed into the heat source to which the sensor is compared against.

Not all sensors can be calibrated on site. Some will need to be sent to a laboratory with equipment offering a larger volume, wider temperature range, or greater accuracy.

Calibration frequency

Calibration brings increased confidence in the measurements being made, and the frequency of calibration needs to be determined to suit the application.

Let us consider a sensor being used with an instrument to verify that a specialist adhesive is stored below -80°C, and failure to observe this impacts the bond strength of the adhesive. Suppose the sensor is checked annually, and all is well for some years. Then, at an annual recalibration, it is noticed the sensor has shifted by a large amount. At what point did the shift occur? The day after the previous check, half way through the year, the day before?

Of course there is no answer, in the same way there is no answer to how much adhesive may be impaired, or how many products to recall. Calibrating more frequently, as well as using multiple sensors, would increase confidence and reduce the risk of a nightmare scenario.

How to choose the right level instrument for applications

rtemagicc_ctl1609_mag_f1_processsensing-level-rosemount-emersonfig1-jpgThere are many level measuring techniques, however they need to be the right fit for the application. See the three key constraints to measuring solids in tanks and vessels.


Companies dealing with bulk solid materials have to measure the contents in vessels and tanks, as do users working with liquids. However, certain obvious differences make the task far more difficult when trying to get an accurate volumetric or mass measurement of solid products. The biggest difference is the way in which solids flow, or don’t flow, contrasted with liquids.

Some solids have sufficient granularity to separate into particles. With these, some may agglomerate into chunks, but the underlying assumption is the material can be poured, at least for the most part. (If a vessel is filled with completely solid material, there are bigger problems than simply trying to measure the volume or level.)

Finding a solid level

Liquids, even those with high viscosity, ultimately come to a uniform level in a container. Solids, on the other hand, form piles. If a pipe or chute is sending granules into a vessel, the highest point will be directly under the pipe. The difference between the highest and lowest point in the vessel may be great, or it may be quite uniform, depending on the material and other factors.

This pile-forming characteristic is quantified as the angle of repose, meaning how steep the sides of the pile can become before part of the pile will slide down (see Table 1). Spherical plastic pellets will not pile up very high because they roll down the sides of their own hill. Other products, even if they aren’t sticky, can form higher piles due to the particle shape or natural cohesiveness. Under most circumstances, few products have an angle of repose below 30 deg or above 45 deg. Even wet sand, if allowed to move freely, will not pile up steeper than 45 deg.



Picture a round vessel with a conical bottom as shown in Figure 1. It is filled from a pipe mounted from the roof equidistant from the center and outer wall. The outlet at the bottom is centered, and the cone walls are sloped at 45 deg. When the vessel is being filled, the product will pile up under the inlet pipe and move toward the outside. When the filling stops, there will be a conical pile with the sides approximating the angle of repose for the material. The lowest point in the vessel will be near the walls, farthest from the inlet pipe. When the outlet is opened, the material directly over the opening will fall out eventually creating a hole as the material higher up moves in from the sides and above to fill the void.

Three solid measuring technologies

Techniques for measuring solids are usually from the top to the bottom, with the level instrument mounted on the vessel’s roof pointed down at the surface of the material. Three of the most common include:

  • Guided-wave radar using a probe to direct the pulse travel
  • Noncontacting radar
  • Acoustic.

Each of these has its own peculiarities related to how it handles the characteristics of solids. Under normal circumstances, all three calculate measurements based on the elapsed time between an energy pulse being sent down and a reflection from a point on the surface returning to the instrument.

With guided-wave radar, it is a very small point, only 1 or 2 in. in diameter surrounding the instrument’s probe. The instrument can’t create a picture of the whole surface from just one point, but for some applications, one point may be enough to receive the information. Noncontacting radar and acoustic level instruments can read a larger area, particularly the latter, but may still yield an incomplete picture. Whether it is sufficient or not depends on the process’s needs.

Understanding instrument constraints

Guided-wave radar instruments, as shown on the left of Figure 1, use a probe designed to extend down into the material. The reading signal travels down the probe, hits the surface of the material, and returns up the probe to provide a very precise reading of the material height around the probe. Because the signal travels down the probe, it can have advantages over noncontacting radar in low dielectric applications.

Some probes are made from flexible cable while others are rigid rods. Flexible probes are better for solids because when large amounts of material start moving, the forces can bend or even break a rigid probe due to the unevenness of movement, particularly when the vessel is filling or emptying.

Pull force is a characteristic generated because a probe embedded deeply into a large volume of material can have an enormous amount of tensile force applied as the material moves while the vessel is being filled or emptied (see Table 2). Probes can be yanked out of the instrument housing, or worse, a well-reinforced probe can simply pull the top of the vessel down. But the tensile force can be calculated to avoid these situations. Depending on the material, frequent movement close to the probe can also cause abrasion and premature wear. Still, in the right application, a guided-wave radar instrument can be a very accurate and economical choice.



Dielectrics and bulk density

Noncontacting radar and acoustic instruments depend on sending pulses throurtemagicc_ctl1609_mag_f1_processsensing-level-rosemount-emersonfig2-jpggh open air to the surface of the material and the timing of the reflections (see Figure 2). The accuracy of the measurement depends on the strength and repeatability of the return signal. The characteristics able to create a strong signal make for major differences between radar and acoustic methods. Radar instruments depend primarily on the dielectric constant (DC) of the material, while acoustic instruments depend on bulk density.

With a noncontacting radar instrument, a pulse of electromagnetic energy is emitted. When the pulse encounters a boundary where there is a change in the DC, some of the energy is reflected back. The boundary in this case is the interface between the air in the vessel and the surface of the material in the vessel, which can be solid or liquid. The higher the DC of the material, the stronger the reflection is.

The surface angle presents a problem with measuring the level of solids. If it is flat, the reflection goes straight back to the instrument, but if the pulse hits a slope, part of it can be reflected to the side of the vessel and not captured (see Figure 3). In most situations, enough of the signal is returned to get a usable measurement, but if the material has a low DC and a high angle of repose, it makes for a difficult combination. Special solids algorithms in the instruments and parabolic antennas can help with measurements in solids applications.


Acoustic instruments have a similar, but different constraint. An acoustic pulse or sound wave produced by the instrument passes through the air space until it encounters the surface of the solid contents of a vessel or the vessel walls. Reflection strength is determined by the bulk density of the material, which is the mass of the substance in a given volume. So if the material surface stays fluffy, it absorbs some of the sound energy, and the reflected waves are not as strong.

Again, situations where this becomes a serious issue are rare, but it is something to keep in mind with some particularly troublesome products. Since the beam is much wider than noncontact radar instruments, the instrument can capture information for average level calculations over the entire surface it sees. On some vessels, the level information can be enough to calculate the volume within 3% accuracy, although larger vessels may need multiple devices to get these results.

Other level-measuring variables

When getting down to specific individual application cases, there are more subtle characteristics in different technologies and instruments. Other considerations capable of influencing method and instrument selection include:

  • Dust levels
  • Product abrasiveness
  • Product corrosiveness
  • Moisture and condensation
  • Inlet and outlet positions
  • Internal obstacles
  • Ambient noise and EMI
  • Frequency of filling and emptying cycles
  • Instrument mounting constraints
  • Minimum and maximum distance.

These are all things that should be discussed with a measurement solution provider when choosing the right level instrument for a specific application.

Creating a topographical model

For many applications, the plant operator may only need a general sense of how much material is in a vessel. If experience suggests a clear picture of how the material tends to pile with low and high spots in the same areas, one point measurement may be sufficient. Other situations may not be as simple.

When the vessel has a large diameter, or where inlets and outlets cause uneven loading due to awkward locations, one or two measuring points may not be enough, particularly when a high degree of accuracy is needed. In those cases, acoustic instruments used alone or in coordinated groups offer a capability to create a more detailed picture.


Since the acoustic instrument information is so complete over the area it sees, it can create a topographical map of the surface inside the vessel. In very large vessels, individual pictures from multiple instruments can be knit together into a very precise larger image covering the surface of the material from wall-to-wall (see Figure 4). Software external to the instruments averages high and low spots when multiple instruments are needed to calculate total volume very accurately. The complete visual image also can warn operators if excessively high or low points are forming, which can indicate moisture contamination or poor material flow within the vessel.

The number of instruments needed to create such a detailed picture is determined by a combination of factors:

  • Vessel diameter—Larger vessels need more instruments
  • Head space—When the material surface is close to the top, one instrument cannot read as large an area
  • Precision requirements—Increasing the number of instruments helps create a more precise picture.

This approach can be an expensive solution since it may require a large number of instruments supplemented by the necessary processing power to do the calculations. However where the material is very expensive, has movement or flow problems, or a very accurate picture is needed, this type of solution can deliver whatever level of precision is needed.

Level measuring factors

Measuring level with solids is more complicated than with liquids because so many measuring techniques simply don’t work, leaving a shorter list of options. The three technologies that have been discussed can cover the vast majority of applications if the process’s needs are understood along with the technology’s limitations.

When a small-area-spot reading is enough, or the material is especially problematic due to low dielectrics, guided-wave radar is accurate and economical, provided the mechanical constraints can be overcome. Noncontacting radar also can provide a slightly larger single-point level reading without worrying about a probe.

When a larger area needs to be read and averaged, acoustic can do the job. The determination of which technology is best for a given application will depend on a number of factors including:

  • Specific material characteristics
  • Installation considerations
  • Measurement needs.

For applications that require precision volume measurements or where actually seeing into the tank can protect the product or provide additional safety, multiple acoustic instruments working together through a supporting software program can draw a map of the material surface from wall-to-wall and may be worth the additional

Advances in wireless remote monitoring

Wireless monitoring is helping users solve problems by integrating new and existing technologies across a common infrastructure to get data into the hands of those who need it—securely.


The use of industrial wireless sensor networks has been growing rapidly in the process industries during the past decade. During this time, many stories have been told of successful implementations in process, reliability, and energy industries as well as in health, safety, security, and environmental monitoring applications. Many users across these industries have found that wireless monitoring technologies provide new ways to improve the performance and reliability of their operations.

Measure things that couldn’t be measured before

The cost of wireless sensing networks is significantly less than wired infrastructure due to reduced cost of wiring, cable trays, input/output (I/O) equipment, and associated design, installation, and maintenance labor. This reduced cost makes it possible to implement new applications that previously weren’t financially justified. For example, tank farm automation projects are now possible because of cost savings of up to 70% from reduced infrastructure, design, and labor required for installation and commissioning (see Figure 1). Wireless level, temperature, and pressure measurements can be installed to monitor the materials stored in these tanks, improving the capability of operations.

Wireless sensing technologies make it possible to measure processes that could not be measured before. New sensors, combined with analytics software are being applied to applications, such as process emissions, steam trap health, relief valve status, and equipment corrosion monitoring. Previously, these applications required manual inspection using handheld equipment or other manual techniques. With manual inspection, identifying the source of process gases that are being sent to a flare can be very difficult. Now, wireless acoustic monitoring allows companies to identify the source and quantity of material being sent to flares (see Figure 2).


An electricity and natural gas utility company implemented a wireless network to enable remote monitoring of outlet gas pressures from four district regulators. The company required quick installation and the cost of installing wires was prohibitive. By attaching WirelessHART interface adapters to existing pressure transmitters, it was able to replace paper chart recorders with digital information displayed on screens in the control room and logged in the historical database. The entire installation was completed, tested, and tuned in three days.

WirelessHART networks also can enable access to smart field device diagnostics that are stranded by legacy systems. Most legacy control systems don’t have I/O hardware that is capable of HART digital communications with smart field devices. Rich diagnostics and sensor data is trapped in these smart devices with no way for monitoring systems to connect to them. Previously, end users have dealt with this by wiring multiplexers, but this approach is complex and costly to implement. Instead, WirelessHART networks enable access to diagnostic information through the use of wireless transmitters installed on smart devices (see Figure 3). For example, control valve diagnostic information can be accessed remotely by technicians for online diagnostics and troubleshooting.



Integrate data across information silos

Wireless data shouldn’t stand by itself. Integrating wired and wireless data into analytics and visualization applications increases users’ ability to do more with the data. Wireless data can be integrated into control systems, data historians, and software applications where data from other sources also are available. Before adding wireless measurements, engineers should take inventory of sensor data that is already installed and add new points to complement existing measurements.

When the data is integrated, flexible analytics and visualization platforms enable experts to derive insights and actionable information. Subject matter experts have a more holistic view of data and can make recommendations based on their education and experience. Purpose-built software tools can be used to apply physics principles or empirical models to deepen the level of analysis.

For example, software with first-principle thermodynamic models can be integrated with a data historian to detect equipment performance degradation as an early indication of mechanical problems. An existing heat exchanger might have flow and process temperature measurements that are used by for temperature control, but would require additional temperature and pressure sensors to be installed for performance monitoring. Existing measurements can be combined with new wireless measurements, where mechanical gauges are replaced with wireless transmitters. By expanding the data set to include all of the available measurements, the thermodynamic models can be used by experts to more accurately detect problems and proactively recommend actions to be taken.

Land and expand

Often, when end users want to get started with wireless monitoring, they are not sure where to start. One approach is to design an all-reaching wireless sensing infrastructure that can enable any monitoring application that one might need—reliability, energy, safety, environmental, and so on. One may design a network of wireless gateways with optimal placement for blanket coverage of operational areas and then layer on applications where needed. This is a great approach if you have the capital available and can justify the investment. Just be sure to choose a standards-based technology that will support a wide variety of measurements and solutions that you can integrate into the same infrastructure.

However, this scenario is not very common. Many operating facilities are capital constrained, and there is a long list of investment opportunities competing for a fixed amount of funding. This scenario makes it difficult to allocate a large amount of capital funds for a facility-wide wireless infrastructure. A more practical approach is to identify the most important problem to solve with a clear return on investment that is easy to quantify. Build the business case for this investment and install a standards-based wireless infrastructure that enables this specific problem to be solved.

Plan the wireless network with an eye on the future and create a design that can be expanded into other areas. Networks such as a wireless mesh network can be expanded easily by adding new measurements online while increasing the reliability and performance of the overall network. By proving the return on investment of a specific issue and designing a network with expansion capabilities, one can install the infrastructure that will support additional wireless monitoring solutions to be added at a later time.

Leverage expertise wherever it’s available

Regardless of the size of the facility, you are not going to be able to staff deep subject matter expertise for every domain. Experts aren’t always available to be physically located where you need them, when you need them. Rather than bearing the cost and time required to bring an expert to the site, wireless monitoring enables data to be collected and sent to the experts-wherever they are located. This enables more effective use of experts’ time, and can make it more economical to retain these domain experts.



Because remote experts cannot be close to the equipment, they cannot see, smell, touch, or hear what is going on. For this reason, more sensor-based measurements are required. Wireless measurements make it possible to collect enough data so that they can make informed decisions without being physically located at the equipment. For example, mechanical pressure and temperature gauges can be replaced with wireless measurements so the measurements can be monitored remotely.

Bigger companies can leverage expertise across multiple sites, and sometimes they will invest in centralized centers of excellence where experts can be co-located for collaboration. This kind of approach is becoming more common in oil and gas, power generation, and mining industries.

Even in these centers of excellence, it doesn’t make sense to develop deep subject matter expertise in all areas. Instead, companies will choose to focus expertise on process monitoring and critical equipment and outsource or partner with external service providers for monitoring in other areas. For example, a power generation center of excellence might have chemical engineers focused on performance monitoring and optimization for turbines and boilers across a fleet of power plants, and outsource monitoring of less critical machinery and valves to a service provider. Experts from a machinery or valve monitoring service provider can analyze the equipment data to detect early indicators of mechanical failures, diagnose the problem, and recommend actions to be taken to slow down failure propagation and to plan maintenance and repair. Whether onsite at a center of excellence or an external service provider, these experts depend on the measurements coming in from the field. Using wireless networks to deliver deeper visibility into the plant enables experts to more effectively contribute to plant performance and reliability.

Reduce security risks

There are several basic options for deploying wireless sensing networks in industrial facilities. One option is to integrate wireless measurements into your control system. This can be done with wireless networks embedded in the I/O subsystem by the control system vendor, or external wireless networks that can be integrated into the control system via protocols, such as ModbusOPC, and EtherNet/IP. This approach is useful when measurements are needed for operators to better control the process. Because the networks are integrated into the control system, they benefit from the same security safeguards used to protect the overall control system. To protect the wireless network, choose a technology that has robust security, including channel-hopping virtual local area networks, encrypted communications, message authentication, white listing, and other security controls.

Another option is to install wireless sensor networks that are separate and independent from the control system. This approach can simplify the security requirements for the monitoring network because it is being implemented in a way that does not introduce connectivity to the control system. Many applications don’t require control system integration because the data isn’t used by operators for control of the process. Instead, wireless sensor data can be integrated into software running on the IT networks where engineers and specialists can more easily access the information. Then, information can be tied to data historians or stand-alone application software focused on solutions such as energy management, environmental monitoring, and regulatory compliance reporting.

For more specialized applications, it is becoming common for vendors to offer connected services based on wireless sensing networks. In this case, the wireless monitoring networks are owned and operated by the service provider and the user pays only a monthly service subscription fee. Vendors provide services based on drop-in monitoring networks that are owned, installed, and operated by the service provider (see Figure 4). These are connected securely through the user’s existing IT network, or installed with Internet connectivity via a cellular router. Appropriate security measures are applied by the vendor, including firewalls, data encryption, and even physical security to prevent tampering.

Stand-alone wireless networks that are used for only measurements, such as acoustics, vibration, and temperature, must be secured for availability, integrity, and confidentiality. However, if these monitoring networks connect to critical control equipment, such as control valves, gas analyzers, or flowmeters, the security needs will be much higher. Even in this case, security technologies, such as data diodes can be used to ensure separation of the monitoring network from external threats.

Untethering data

In this time of digital transformation, the companies that use technology in new ways are the ones that gain a competitive advantage. Merely adding measurement points through wireless monitoring won’t reset users’ expectations to achieve new business goals. When users begin strategically using wireless technology to complement their wired infrastructure to address previously unsolvable issues, they can start to advance the performance and reliability of their entire operation.