FAQ - Frequency Response Analyzers

The electronic properties of a system can be defined in terms of its ability to store and transfer charge (i.e. its capacitance and conductance). The use of electrochemical impedance spectroscopy (EIS) records the response of the system to a small applied perturbation (i.e. AC signal), over a pre-determined frequency range. 

The applied AC voltage and the resultant AC current are measured and the impedance calculated (Z* = V / I). The technique is non-destructive and is particularly sensitive to small changes in the system. To obtain a response, electrodes are placed in contact with the system of interest and a sinusoidal voltage applied. This produces sample polarization, the resultant current having the same frequency but different phase and amplitude. By measuring the complex impedance , Z*, (i.e. the ratio of the applied voltage to the resultant current) and separating the real and imaginary terms, Z' and Z'' (i.e. conductance G and capacitance C) may be calculated. 

Z* = V / I = V sinwt / I.sin(wt + q) 
Z* = a. cos.q + b.sin q = Z' + Z'' = 1/ G + 1/ wC 
|Z| = (a 2 + b 2 )0.5 (q = tan-1 {b/a}) 

These results then allow the permittivity (e' ), loss factor (e''), dissipation factor (e \ e'' ) and ionic mobility (s = eowe'') to be calculated. These parameters relate to the dielectric measurement of materials giving information on molecular structure and dipole alignment. By studying the response of a system over a range of frequencies it is possible to analyze reaction mechanisms and material characteristics.
The use of 1260A in stand-alone mode (i.e. not connected to the 1287A Electrochemical Interface) is common but, to obtain effective results in this mode, modification of the instrument set-up is required. Insure that the shield of the generator output is connected to the current input shield; this completes the generator circuit and provides a return path for the current enabling effective data acquisition.
The use of 'point to point' measurements is to select and measure from any selected point to any another in a circuit, i.e. measure the ratio of Vin against Vout without breaking the feedback loop. The applied voltage undergoes a transfer function which modifies (in gain or phase) the output voltage level. The standard applications of 'point to point' measurement are servo tests and electrical component testing. 
To check that the FRA is operating properly it is recommended that the instrument is tested in stand-alone mode. A series of simple tests performed using front panel operation, enable the user to check the instrument is working correctly. 

(a) Using the front panel keys a 1 volt amplitude is programmed and the frequency swept over the desired frequency range (it is suggested to scan between 1MHz to 1Hz, lower if needed). 

The generator output is connected to channels 1 and 2 via a 'T' connector using BNC cables. The sweep is completed and V1/V2 displayed. The result shown should be 1 throughout the sweep, with a phase value of zero degrees. The experiment should then be repeated displaying only the V1 value, the voltage displayed should be approximately 1 (although this may vary slightly at high frequency). This can then be repeated displaying V2 to check that similar results are obtained. 

(b) The generator output can be checked via connection to an oscilloscope (it is important to make sure that there are no DC offsets). This enables the user to determine whether the generators and analyzers are functioning for the input range. 
On this website there is a free software package called FRA that you can download to run functional tests on your FRA. Click here to locate it. The functional test described below is for determining if the generator and voltage analyzers of your FRA are generating and measuring AC voltage correctly 

Install and start FRA software-Click on System and select your FRA and GPIB address, click Save/Test FRA, then Exit back to the main screen 

GPIB Set Up Screen 

Click on Transfer function and select single channel. Click on channel and select channel 1. Connect the generator output to channel 1 Hi (Input Vi Hi) using one of the 1 meter BNC cables that came with your instrument. 

Select Generator and set the AC amplitude to 1 and the frequency range from 100 kHz-1 Hz.

Click on exit and then click on Measure Sweep. The result you get for magnitude should be very close to 1 (+/-5%). Regardless of the result you get, you should then repeat the procedure for Channel 2 Hi (input V2 Hi). If both channels show the same good result then there is nothing wrong with your generator or voltage inputs. If either or both show a bad result your instrument may need service and you should contact Solartron Analytical technical support.