An Easy Method for Salvaging Thermal Conductivity Detectors Recently during a laboratory session, the gas flow on the reference side of om Gow-Mac Series 550 Gas Chromatograph was not turned on. The resistors on the reference side apparently overheated and this changed their resistance from a value of -360 to -380 (measured cold). This small change in resistance was enough to prevent the instrument from being zeraed at low attenuation (i.e., high sensitivity). Since both resistors on the reference side were in the same environment, it seemed likelv that their resistance had chanced . hv. the same amount. By exchanging one of the resistors on the reference s ~ d with e one on the sample side, the Wheatstone bridge circuit was brought back into balanceand i r was now posaihle tu zero the inatrurnent at its highest sensitivity. Thur, it was necessary
to exchange the diagonally located resistors in the detedor block and to rewire the resistors into their proper circuits. Although this technique may not work all the time, it is worth trying since a balanced set of resistors costs -$150. Peter Ronman Walter Sallstrom Division of Natural Sciences SUNY College at Purchase Purchase. NY 10577
Volume 61
Number 9
September 1984
813
