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BinMaster PROCAP capacitance sensors from HMA INSTRUMENTATION detect the presence or absence of material in contact with the probe by sensing a change in capacitance caused by the difference in the dielectric constant of the vessel material and air. These sensors must be able to sense very small changes in capacitance, typically one picofarad.
To sense such a small capacitance change, competitive manufacturers often use electronic circuits incorporating frequency shift oscillators and balanced bridges that must operate at high frequencies in the RF range. Most capacitance sensor manufacturers use frequencies between 100 KHz and 2 MHz.
BinMaster’s capacitance probes use a unique discharge time constant detector circuit which allows sensing capacitance changes less than one picofarad without the need for radio frequencies.
PROCAP capacitance sensors operate at approximately 6 KHz, well below the RF level and therefore are not subject to FCC regulation. Plus, because the PROCAP sensors operate at such a low frequency, they will not interfere with nearby electronic plant equipment and are not susceptible to interference from other equipment.
PROCAP capacitance probes use advanced integrated circuit technology operating at a low frequency to achieve both high sensitivity and stable calibration. The probe uses a simple timing technique that compares the discharge time of the probe capacitance to that of a reference capacitance. The probe’s outstanding stability results from several factors.
A single integrated circuit makes the critical timing comparison. Temperature variations have an equal effect on the timing of both the probe and reference capacitance and, therefore, cancel.
The time interval at which the discharge comparison is repeated is not involved in the sensing process, making calibration independent of oscillator frequency and stability.
Both the probe and the reference capacitance discharge are from a common voltage level. This makes calibration insensitive to power supply voltage variations.
Equal internal capacitance in both the probe and reference circuitry make any temperature dependent changes to these component values cancel. In addition, these internal capacitors have zero temperature coefficients and are physically located together to assure they are at equal temperatures.
New calibration stability, along with static discharge survival, and RF immunity are three of the main reasons why BinMaster probes outperform the competition