comparators were tired with varying results another method that may be used is to calibrate each board containing the circuit with a reference humidity in this case a known relative humidity can be established and the frequency of each oscillator on each board can be measured the microprocessor on each board would then have a different u201c look up u201d table to translate the frequency measured to a humidity value this method may require more initial set up time however the advantage of this method is that the parts used on these boards do not have to be as closely matched as in the other method the use of a humirel ths1101 humidity dependent capacitor and a philips 555 timer as a comparator and two 1 tolerance resistors along with a microprocessor configured in a similar circuit as fig1 resulted in a 25 variance in rh between several boards this was not accurate enough to track tape failures due to humidity without calibration to a known rh the best solution used a general eastern instrument 39 s gcap 2 s c humidity dependent capacitor c 102 and a philips lm393 comparator ic 102 with high precision resistors 0 1 for r 102 r 104 r 106 and r 108 the variation between boards using this combination showed only a variation of u2212 6 in rh this degree of consistency between boards made it possible to track failures due to rh without calibrating each board to a known rh the foregoing description of the present invention has been presented for purposes of illustration and description it.