Industries Information

 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.