Table I. Bange of parameters of solion linear flow detectors. 



Parameter 



Cathode acoustic resistance 



Current sensitivity 



Pressure threshold 



Frequency range 



Dynamic pressure range 



Background power consumption 



Maximum signal output power 



Operating temperature range 



Maximum temperature coefficient 

 of sensitivity 



Maximum size - diameter 

 thickness 



Maximum weight 



Range of Values 



icA-io? 



0-300 



0.01 to 100 



0.0001 to 30 



1:1 to 30,000:1 



10 to 1,800 



up to 27 



-10 to +30 



+2.5 



3.0 

 0.75 



8.2 



Units 

 acoustic ohms 

 microamp/dyne/cm 

 dynes/cm 

 cps 



microwatts 

 milliwatts 

 °C 



inches 

 inches 



a typical solion linear detector, operating in 

 the linear region, it is interesting to note the 

 volume flow sensitivity. If an iodine concen- 

 trate of 1.0 normal iodine is used, from Eqn. (6) 

 it can be seen that a flow of 10 cc/sec will 

 produce an output current of 100 microamps . This 

 offers an extremely sensitive flow detection 

 capability. 



A comment should be made regarding one other 

 characteristic of the linear flow detector. If 

 an excessive differential pressure is applied to 

 the transducer the flow rate exceeds the linear 

 ion reduction capacity of the cathode electrode. 

 This does not cause the output current to "clip, " 

 but causes the output current to increase as the 

 square root of the flow above the linear range. 

 The flow signal is not "lost" but simply modi- 

 fied. In this manner pressures far in excess of 

 the linear range can be monitored and even mea- 

 sured with proper corrections of the output 

 signal. 



Linear flow detector transducers have been 

 built with a wide variety of parameters . These 

 parameters are given in Table 1. Although a 

 wide range of values is indicated, all combina- 

 tions of extremes are not obtainable in a single 

 detector. 



NONLINEAR TRANSDUCERS 



The flow detector just discussed is a so- 

 called "linear" flow detector transducer. It 

 operates on two principles: (l) linear hydraulic 

 flow and (2) linear electrochemical response. 

 By proper design of both the acoustic (flow) 



system and the electrochemical system, various 

 nonlinear relationships can be obtained. 



Eqn. (7) indicates an output current that is 

 linearly related to pressure. If the acoustic 

 circuit is modified to become nonlinear with 

 pressure, say by inserting an orifice of proper 

 design, then R is not constant but becomes a 

 function of pressure: R = R(p) . 



Eqn. (7) also assumes that the cathode elec- 

 trodes are behaving as linear detectors. By 

 proper design of the cathode electrode structure, 

 various nonlinear ion reduction responses, such 

 as the square root response mentioned, can be 

 obtained. With a combination of both acoustic 

 and electrochemical nonlinearities, a wide range 

 of pressure-current relationships can be obtained 

 such as square root, linear, exponential, square 

 and higher powers (powers up to k have been 

 measured) . By removing an anode from one bulk 

 fluid chamber and replacing it with a scavenger 

 cathode electrode, an output current sensitive 

 to flow in only one direction can be obtained. 

 Therefore, it becomes a rectifying pressure or 

 flow detector. 



Other unusual effects and responses can be 

 obtained although some of these effects are 

 undesirable and difficult to remove from a 

 desired response. 



APPLICATION OF S0LI0NS 



Because of its extreme sensitivity at low 

 frequencies, along with the stable properties of 

 a redox electrochemical system, the solion is 



166 



