The M1715A high precision frequency counter module provides individually isolated field inputs to two 32-bit frequency counters. The counters are designed to operate in the range 1Hz to 5kHz and return the period in nanoseconds of each input to an accuracy of better then 15ppm.

A target application for this module is as interface to vibrating tube densitometers to allow the highest accuracy of frequency to be measured in oil and gas custody transfer applications.

Liquid density is one of the many parameters to be accurately measured for product quality control, custody transfer, process control, or liquid interface detection purposes. In the hydrocarbon industry, the vibrating tube densitometer is most common. In this type of densitometer, a tube of known mass is vibrated at its natural frequency. As the tube is filled with the process fluid, the frequency will be damped proportionate to the density of the material. Other variables, such as specific gravity, molecular weight, Brix and concentration can be derived from this measurement if required. The mass is related to the mass of the tubing plus the mass of the fluid inside the tubing. As the mass (or density) of the fluid in the tubing varies, the natural frequency varies. Because of the relative mass of the tube to the process fluid in the tube, the measurement of frequency must be highly accurate to achieve satisfactory results. The high accuracy of the Maxiflex 2PFC module makes it ideal for this measurement application.

The 2PFC module should be used in conjunction with dedicated software to be used as part of the user application. For use with Isagraf compatible CPUs use the Omniflex supplied function block “cn74_t”. For use with Forth compatible CPUs, ask Omniflex for the necessary eziForth words.

Each input may be configured by links inside the module to either be a 3-5V dc, or a 9-30V dc input to support the widest range of densitometers.