174 



(1) A calibration tank having 

 provision for temperature control and 

 rapid circulation of the water has been 

 constructed. In it, approximately 120 

 gallons of water come in contact only 

 with rubber or plastic (except for three 

 lead-sheathed heaters)and is circulated 

 by a 40 gallon per minute plastic pump. 

 Plastic coated refrigeration coils pro- 

 vide means of operating below room 

 temperature. When this tank can be 

 placed in operation, it should provide 

 the means of presenting a homogeneous 

 environment to test instrument and 

 standards, thus furnishing a measure 



of the reliability of the instrument under 

 static conditions. 



(2) Three characteristics of the 

 H-type conductivity cell were measured 

 in the laboratory where considerably 

 more control over environmental con- 

 ditions and measuring circuits is possi- 

 ble than with the complete CTI. The 

 characteristics measured were frequen- 

 cy and temperature coefficients, and 

 cell stability. 



6 8 10 12 14 16 



C.T.I. Conductivity Scale 



Fig. 3, CTI field calibration. Com- 

 puted conductivity obtained by using 

 titration chlorinity results, CTI tem- 

 perature, in the Thomas, Thompson, 

 and Utterback interpolation formulas. 

 Data obtained over several months 

 period during winter of 1951-52. 



The H-type conductivity cell was 

 set up in a thermostated plastic contain- 

 er. The energizing and measuring cir- 

 cuit was a conventional alternating cur- 

 rent bridge composed of a variable fre- 

 quency oscillator, balancing resistors 

 and capacitors, and a vacuum tube volt- 

 meter. Provision was made to meas- 

 ure the stability of the circuit itself by 

 the substitution of a. fixed RC network 

 in place of the conductivity cell. With this arrangement the effects on the ap- 

 parent conductance of the H-type conductivity cell produced by various methods 

 of cleaning the cell, by changes in frequency in the range 70 cps to 3000 cps, and 

 by changes in temperature in the range 16° to 32°C were measured. The re- 

 sults of some of these measurements are summarized below. 



The conductance of the cell was measured at 70, 150, 400, 1000 andSOOO 

 cps, at five temperatures as the cell and solution were warmed from 16° to 32° 

 C and at the same temperatures while cooling through the same temperature 

 range. The measurements were made over a period of approximately five 

 hours. The results are shown in figure 4. It will be seen that the effect of 

 variations in frequency at any one temperature are rather large. In the inter- 

 val 70 to 150 cps, an apparent change of 0.01 millimho (approximately 0.01 

 CI °/oo) would be produced by a frequency change of 0.8 cp. Transient frequen- 

 cy changes of about 1.0 cps are not uncommon with generators normally used on 

 shipboard. The results of these measurements prompted the inclusion of a 

 frequency meter in the control box now used with the CTI (the topmost box in the 

 stack shown in Figure lA). Nevertheless, the effect of changes in frequency by 

 itself apparently cannot account for the approximately 0.05 CI °/oo spread meas- 



