Pressure recorders are available in two basic types: strain gauges for general usage and quartz gauges, with higher resolution, where better accuracy is required. Strain or quartz elements provide a primary amplitude signal, from which pressure is inferred.
Recorders are calibrated in an oil bath, where temperature and pressure are applied by a certified source. Any gauge deviations are corrected employing a calibration equation.
Electronic recorders measure absolute pressures and are available in a variety of ranges (i.e. 93–20 000 kPaa). Try to choose gauges so pressures will fall between 20 % and 80 % of the range. Below 10 % of the range pressure data are much more prone to noise.
A clock is required to obtain a data sequence. Clocks last as long as the batteries, but do malfunction once in a while, for various reasons (slow down, speed up, or stop).
Clock sample frequency can be set on electronic recorders. Rapid sampling is fine for short tests or during times of rapid pressure change but can lead to excessive data file sizes in long tests. Slower sample rates can miss important data points, such as the final flowing pressure, but can allow for longer tests, as memory and battery power will last longer.
Temperature of the strain or quartz element must be known, so a thermometer is installed and provides another primary input signal. Note, then, that calculated pressure is actually a secondary product.