Industries Information

Kerk Motion Products’ RGSW and RGSWX slides offer precision motion in a convenient package Kerk Motion Products has released RGSW and RGSWX slides. The slides provide both exceptional value and linear motion performance to engineers in demanding industries such as packaging, assembly, medical and life sciences, semiconductor manufacturing, and factory automation. Like the original RGS slides, the RGSW and RGSWX slides offer precision motion in a convenient package. This article was originally published on Engineeringtalk on 17 August 2007 at 8.00am (UK) Related stories Actuator is e-mech alternative to pneumatics Linear actuator incorporates high precision, long life, innovative design and patented technology in a value-priced rod-type device Their patented design allows high linear speeds without critical speed concerns. Kerk’s RGSW and RGSWX slides offer thicker and wider bases than the original, more compact RGS slides. Both the RGSW and RGSWX series include direct sensor mounting systems and the RGSWX slides with direct motor mounting can accept NEMA-frame motors without any modifications or additional fabrication. Requiring no maintenance or lubrication, the anti-backlash slides can be manufactured in lengths up to 2.5m. Longer lengths are possible on a custom basis. The Kerk RGSW and RGSWX enhance Kerk’s product range and provide a more complete solution for customers requiring integrated product features. Additional carriages can be mounted on the rail for additional support required by larger loads or unusual mounting configurations.

 Ion specific meters are millivolt meters that interface with ion selective electrodes (ISE). The meters take the potential generated by the electrode and convert it into units of concentration. A pH meter that also measures millivolts can be used to interface with an ISE. Most ISEs are combination electrodes that have the reference electrode built into the body of the ISE, however some ISEs require a separate reference electrode. In this case, the pH/mV meter must have a pin-connector to attach to the reference electrode.

To order the proper ion specific meters, the user must know certain specifications. First is the concentration the ISEs are to measure. Also the number of ISEs to be attached to the meter. Other important options for these instruments are other measurements they can perform, typically of temperature, pH and oxidation-reduction potential (ORP), also known as redox. These instruments can have some controller functionality such as set limits, regulator, P/PI/PID as well as control relay output.

Mounting options for ion specific meters are quite varied. They can be handheld meters, larger portable meters with wheels or handles for carrying, and modular for interfacing with sensors of different input ranges. Other styles commonly available are specially designed for lab or benchtop use and others for field or in-situ applications. Some of these meters are designed to be mounted in a panel.

Displays for the instruments can be analog meters, a numeric or alphanumeric digital display or video, a CRT or LCD style. Another option is to have no local display at all and have the data gathered by another instrument. Likewise, the user controls can also be analog or digital or can be operated through a host computer. To simplify the instruments, preprogrammed devices without user controls are available.

Electrical output options are the standard voltage and current outputs as well as an analog frequency or a change in state of switches or an alarm. Serial and parallel ports can help connect these instruments to a host computer.

Some features available for many ion specific meters include battery power for greater portability and built-in signal processing filters. Built-in calibration ability and self-test functions are also available, as are event triggering and ratings for extreme environments.

Ion selective electrodes (ISE) measure the potential of a specific ion in solution. This potential is measured against a stable reference electrode of constant potential. The potential difference between the two electrodes will depend upon the activity of the specific ion in solution. This activity is related to the concentration of the specific ion, therefore allowing the end-user to make an analytical measurement of the specific ion. Several types of sensing electrodes are commercially available. They are classified by the nature of the membrane material used to construct the electrode. It is this difference in membrane construction that makes electrodes selective for a particular ion.

The most important specification for ion selective electrodes is the type of ion the user needs to detect. Also important are the concentration range and accuracy, pH range through which the electrodes can operate and the response time, which is typically given as the time needed to reach 95% of the final value. Ion selective electrodes may be half-cell models that require a separate reference electrode, or combination models composed of two parts, the measuring electrode and the reference electrode.

Handheld or portable configurations allow ion selective electrodes to be used with ease in laboratories, where the operator may be testing several different samples. Insertion style electrodes are often inserted into process piping through a tapped hole in the pipe or bulkhead. Flow-through styles fit directly into the pipeline and become an integral part of it via some connection such as a flange or other fitting.

Samples read by ion selective electrodes may be aqueous, non-aqueous, or dry, and the electrodes may have many different types of membranes. Each type of membrane has its own unique characteristics that make it the best choice for a particular application. The most common choices for membranes are glass, solid state, liquid-ion exchange, PTFE/gas sensing, ISFET and plastic. Typical features for ion selective electrodes are built-in temperature sensors and temperature compensation.

Instrument calibration service providers calibrate various instruments including many types of process monitoring devices and analytical equipment including, flow instruments such as flow meters and sensors, gauges, totalizers or valve position indicators; pressure and vacuum instruments such as pressure sensors or gauges, meters, transducers or vacuum pumps; force, weight or mass instruments including strain gauges, load cells, scales or torque monitors; temperature instruments including thermocouple, RTD or thermistor type devices; humidity instruments including absolute or relative humidity, moisture content or dew point measuring devices; multimeter or electrical meters, either analog or digital; physical or dimensional instruments such as calipers, and micrometers, fiber optic or lightwave instruments including multiplexers, analyzers, isolators etc; rf or microwave instruments such as transmitters, receivers, antennas etc; generators; power supplies including any AC or DC power supply or conditioners; oscilloscopes or scopes or chart recorders; and signal or function analyzers.

Providers of instrument calibration services may have one of several calibration quality requirements.  These requirements include ISO / IEC 17025, ANSI / NCSL Z540-1, A2LA, ISO 9001, ISO 9002, NIST, or GMP / FDA.  ISO 17025 addresses the proficiency of the organization to perform the testing and calibration activities. It is a standard geared towards technical qualification and deals heavily with measurement uncertainties. This is layered on top of an ISO 9000 certification, which is a standard, used for total company quality system.  Formerly MIL-STD 45662A, American National Standard ANSI / NCSL Z540-1 is a requirements document titled "Calibration Laboratories and Measuring and Test Equipment - General Requirements."  A2LA is the American Association for Laboratory Accreditation.  A2LA accreditation is defined as formal recognition of an organization’s technical competency to perform specific tests, types of tests, or calibrations.  ISO 9001 sets out the requirements for an organization whose business processes range all the way from design and development, to production, installation and servicing.  ISO 9002 is for an organization, which does not carry out design and development. It does not include the design control requirements of ISO 9001 - otherwise, its requirements are identical.  Calibrations are traceable to National Institute of Standards and Technology.  GMP, or Good Manufacturing Practice, is a quality requirement for instruments involved in sanitary processing; such as pharmaceuticals or foods. FDA, or Food and Drug Administration, is a similar quality requirement.

Specific services offered by providers of instrument calibration services include, rapid turnaround, on-site calibration, pick up and delivery, calibration documentation, in-house contract lab services, and online documentation.  Rapid turnaround means the supplier offers quick turnaround on instrument calibration services, typically in a few days.  A supplier offering on-site calibration has personnel and/or equipment for on-site calibration work, eliminating the added expense of taking the instrument off line and shipping it.  The supplier offers pick-up and delivery services to minimize cost and time associated with using in-house personnel.  Documentation or test reports show calibration information such as "as found" and "as left" data, next scheduled calibration, etc with calibration documentation.  A supplier that offers in-house contract lab services has capabilities and resources for setting up an in-house contract lab for supplier - minimizing any downtime or lag in getting instruments quickly calibrated.  Supplier has online documentation system to access history, calibration certifications and recalibration notifications.

Conductivity meters, dissolved solids meters, and resistivity meters are analytical instruments that measure either conductivity, the amount of dissolved solids, or resistivity of a liquid sample. The meters can measure either one or a combination of these qualities. Because the qualities are so similar, combination meters are common instead of a meter that measures just one of these.

Conductivity in units of mhos/cm or Siemens/cm is a measure of water’s ability to transmit an electrical current. It is a gross, indirect measurement of the concentration of ions and consequently can be used to estimate total dissolved solids (TDS) levels. TDS is a measure of the dry mass (mg/l) of all the dissolved solids in water. Most of the colloidal particles will be included in a total dissolved solids measurement. Resistivity is the reciprocal of conductivity.

Typical specifications are the measurement range, accuracy and the temperature of the process media being measured. Conductivity meters, dissolved solids meters, and resistivity meters may have some controller functionality such as set limits, regulator, P/PI/PID as well as control relay output.

Mounting options for the instruments are quite varied. Conductivity meters, dissolved solids meters, and resistivity meters may be handheld meters, larger portable meters with wheels or handles for carrying, and modular for interfacing with sensors of different input ranges. Other styles commonly available are specially designed for lab or benchtop use and others for field or in-situ applications. Some of these meters are designed to be mounted in a panel.

Displays for the instruments may be analog meters, a numeric or alphanumeric digital display or video, a CRT or LCD style. Another option is to have no local display at all and have the data gathered by another instrument. Likewise, the user controls can also be analog or digital or can operated through a host computer. To simplify the instruments, devices without user controls are available, as well.

Electrical output options are the standard voltage and current outputs as well as an analog frequency or a change in state of switches or an alarm.

Features available for many conductivity meters, resistivity meters and total dissolved solids meters include temperature compensation, battery power for greater portability and built-in signal processing filters. Built-in calibration ability and self-test functions are also available, as are event triggering and ratings for extreme environments.

Dissolved oxygen meters are analytical instruments used to measure the amount of oxygen dissolved in a unit volume of water. It is an important indicator of the degree of usefulness of a sample of water for a specific application.  Air consists of 21 percent oxygen and approximately 78 percent nitrogen by volume. Oxygen dissolves poorly, and can only exist in water in low concentrations. Even so, dissolved oxygen (DO) is essential for the respiration of a wide variety of animals and bacteria in the aquatic environment.  The accurate measurement of dissolved oxygen is critical to many other applications including water treatment plants, sewage treatment works, effluent activated sludge process, river monitoring, fish farming, and any other field where water quality is important. Dissolved oxygen is also one of the key measurements in biotechnical processes, and is essential to maintain quality of the finished product.

Dissolved oxygen meters interface to one of three common types of dissolved oxygen sensing probes: polarographic sensors, galvanic sensors or optical fluorescence sensors.  Polarographic sensor technology uses an external voltage. The difference in potential between the cathode and anode is less than 0.5 volts. This includes Ross and Clark polarographic types.  A galvanic probe uses requires no external voltage. The difference in potential between the cathode and anode is greater than 0.5 volts. Galvanic probes are more stable and more accurate at low dissolved oxygen levels than polarographic probes. Galvanic probes often operate several months without electrolyte or membrane replacement, resulting in lower maintenance cost.  The optical fluorescence sensor does not use up oxygen during measurement, therefore it does not require stirring.  The device is extremely suitable for long-term measuring periods in groundwater. It is not sensitive to contaminants, sulfurous compounds, or aging.  The sensor has a special coating with fluorescent properties. When light is exposed to the coating it causes fluorescence.  After the exposure of light, the coating continues to produce a short afterglow. The level of oxygen present in the water determines the duration of this fluorescence or afterglow.

Important specifications for dissolved oxygen meters include measuring ranges and accuracies.  Handheld or portable configurations allow dissolved oxygen meters to be used with ease in laboratories, where the operator may be testing several different samples.  Laboratory or benchtop and panel configurations allow for fixtured or permanent setups, while in-situ or field mounted dissolved oxygen meters are useful in remote sensing applications.

Typical features of dissolved oxygen meters include battery packs, filters, event triggers, built-in or self-calibration, extreme environment housings and self-tests or diagnostics.

Dissolved CO₂ instruments are analytical devices that measure the amount of carbon dioxide (CO₂) dissolved in a liquid sample such as water. They typically include a submerged probe that is covered by a thin organic membrane. When the probe is submerged in the liquid sample, carbon dioxide diffuses through the membrane at a rate proportional to the partial pressure. Increasing the partial pressure increases the diffusion amount. The liquid sample is considered to be saturated when the molecular activity of the carbon dioxide equals that of the liquid. Air contains only 0.035 % carbon dioxide by volume; however, CO₂ is nearly 30 times as soluble in water as oxygen. Carbon dioxide moves across the air-water interface according to the same physical process that affect the dissolving of oxygen. Both temperature and pressure affect the diffusion rate measured by dissolved CO₂ instruments. Accuracy and diffusion range are typically measured in parts per thousand or parts per million.

Dissolved CO₂ instruments vary in terms of user interface, features, and output options. Some devices provide analog or digital displays. Others include devices such as cathode-ray tubes (CRTs), liquid crystal displays (LCDs), or flat panel displays. User controls may consist of knobs or potentiometers mounted on a simple front panel. Digital front panels are programmable and work with a keypad. Some devices are battery-powered, self-calibrating, or equipped with self-test diagnostics. Others are triggered by events or include signal processing or filtering. Output options include analog voltage, analog current, analog frequency, and switch or alarm relays. Analog voltage outputs are a simple (usually linear) function of the measurement. Analog currents use feedback to provide an appropriate current regardless of variables such as noise and impedance. Analog frequencies use continuous physical variables such as voltage amplitude or frequency variations to transmit information.

Important specifications for dissolved CO₂ instruments include the maximum number of input channels, the maximum bandwidth, the resolution in bits, and the sampling frequency. Environmental considerations include the operating temperature, minimum shock rating, and maximum vibration rating. Dissolved CO₂ instruments that feature a computer interface are commonly available and may include non-volatile memory or removable hard drives. Communication protocols and bus types for dissolved CO₂ instruments include ARCNET, AS-I, Beckhoff I/O, CANbus, DeviceNet, Ethernet, Foundation Fieldbus, general-purpose interface bus (GPIB) or IEEE 488, InterBus, PROFIBUS, and SDS.

Density and specific gravity instruments are meters used to determine the density and specific gravity of a mixture that may be solid, gas, or liquid.  The density range (mass per volume), accuracy, and response time characterize most of these instruments.  Simultaneous measurements and user interfaces are also important in choosing the proper density and specific gravity instruments.

Density digital meters that use the principle of either oscillating tubes or radioactive adsorption to determine density and specific gravity are the most common types of density and specific gravity instruments.  An oscillating tube is a hollow glass tube that vibrates at a certain frequency.  The vibration frequency changes when the tube is filled with a sample.  The higher the mass of the sample, the lower the vibration frequency.  This frequency is measured and converted into density. A built-in thermostat controls the temperature (no water bath required).  A thermostat is often necessary since the density of the sample could be changed by temperature variations.

Radioactive adsorption, the use of gamma rays or x-rays to determine density, is helpful in applications such as piping or mining where intrusion into the system may be costly.  Energy is emitted by a source that passes through the pipe walls and the process material.  The process material adsorbs the energy.  The amount of energy reaching the detector varies with each material.  Electronics convert this energy reading to a density measurement.  This method is particularly effective in process applications that involve extremely high flow rates, high pressure, and high / low temperatures.

Another noninvasive method used by density and specific gravity instruments includes microwave phase difference measurement. Microwave phase difference exploits the way a fluid’s density affects the propagation of microwaves when they pass through it.  This allows a reliable measurement of the fluid’s density by monitoring the difference in microwave phase between the original wave and the one that passed through the measured fluid.  Measuring fluid density by observing a wave’s phase difference is unaffected by flow velocity and/or is not affected by the contamination and/or bubbles.  This technology is effective in various applications where determining the consistency of suspended solids, slurries, and sludge is necessary such, as in the pulp and paper and wastewater industries.

Suspension methods include measuring the density gradient and the Schlieren method.  Density gradient is measured when two liquids of different densities are layered in a glass tube so that over time, diffusion results in a vertical density gradient.  The Schlieren method involves immersing a liquid-filled tube in another liquid,  the liquid will only flow horizontally from the tube if the densities of the two liquids are equal.

Density and specific gravity instruments provide various readouts are available based upon the user’s needs.  Analog and digital displays are available on portable instruments.  Display parameters may include Brix, Plato, % alcohol, API gravity, percent solids, percent mass, and percent volume may be available.  Other options may include computer interfaces and software for programming customized concentration or specific gravity tables, data analysis, and/or control.

Density and specific gravity instrument systems range from laboratory applications where autosamplers and cleaning components are integraged to tank management systems for remote monitoring to flow transfer and control applications.

Calibration of density and specific gravity instruments is dependent upon the technology type used.  Nitrogen gas or water at specific temperatures and pressures may be required prior to using the instrument.  Some density meters may include a calibration certificate.