Percent Concentration Sensors ISC40

Why Measure Conductivity?

Conductivity measurement is a reliable indicator of the concentration of most acid or base solutions. The desired chemical concentration is achieved using a two stage mixing procedure. During the first stage, the flow ratio control unit on the missing tank is set to provide (x) gallon per minute of the full strength solution and (y) gallons per minute of water. These values are adjusted to produce a concentration value which is slightly weaker than the desired value. This ratio control must include alarm capabilities to indicate "low flow" conditions for both the full strength solution and the water in order to prevent wasted chemicals or hazardous situations. 

At the second stage, a conductivity sensor and analyzer function as a "trim control". This combination adds small amounts of full-strength solution to the mixing tank to produce the exact concentration desired.

For example, to produce a 4% caustic solution from a large bulk caustic supply at 50%, the flow ratio controller is adjusted to make a 3% solution and the conductivity information is used to add additional caustic to achieve the 4% concentration.

Conductivity is a very reliable index of the concentration for most acid and base (caustic) solutions. The graph to the right shows the correlation between conductivity and concentration for four common solutions. 

For most solutions, there is a peak conductivity value. Before this peak value is reached, conductivity correlates positively with concentration; after the peak, it correlates negatively. So, if the concentration range passes through the peak for that chemical the conductivity value (except the peak value) represents two different concentration values. Therefore, it is mandatory that any application near the peak of a particular solution be carefully controlled.

In determining the proper loop components for a particular application, the material of construction will be of primary concern. A chemical resistance chart should be consulted (see Table 1), or an application data sheet completed and sent to the factory in order to insure an installation that will be suited for the intended application.

ISC40FF/ISC40FS/ISC40FD Holders 

This program includes flow fittings and their subassemblies for in-line or direct mounting of conductivity sensors in piping systems. A wide choice of construction materials gives the user the best solution for any process considering chemical resistance, pressure and temperature specifications.

• Wide choice of construction materials.
• High degree of standardization to all cells.
• Easy mounting, service and removal or replacement of sensors.
• Electrolitically polished stainless steel designs for optimal corrosion resistance.
• Available with flange adapters.

Model PR10 Retractable "Hot-Tap" Holder

On-line measurements often present extra challenges, especially when routine maintenance is required. The PR10 is ideally suitable for applications where the sensors must be removed without interrupting or shutting down the process. Without any special tools the PR10 can be retracted safely from the process at pressures up to 5 bar (72 psi). The PR10 is a universal retractable assembly that can be used for all liquid measurements. The PR10 is designed to accept any commercially available pH/ORP or dissolved oxygen sensor that has a PG13.5 connection while still being backwards compatible with old Yokogawa electrodes.

For ease of use optional flush ports are available. In the retracted position the sensor can be kept moist, cleaned or even calibrated. This can all be done without process interruption or disassembly of the armature.

•  One model for pH/ORP, dissolved oxygen, conductivity and inductive conductivity sensors
• All commercially available pH electrodes, such as PG13.5, SMART sensors, Vario Pin, YEF and DIN connectors can be installed in the PR10.
• Integrated protection cage
• A "scraper" is built-in to each assembly to effectively scrape or wipe off the
  process from the PR10's shaft as it is being retracted from the process.
• A safe "through the valve" insertion and retraction design
• Simplified installation by optional ball valves with flanged or tapered connections
• Optional flush port accessories makes it easy to keep sensors moist (pH) and clean, and also provides access for calibration if desired.

Calibration Standard Solutions