I'm needing to make some measures of low frequency impedance (1-1kHz range) of some liquid solutions and plaster samples.
1) What would be a good tool for measuring impedance for around $500? I see mostly very high price ranges for impedance analyzers ($2k or more).
2) Also, when shopping for LCR meters or impedance analyzers, what should I look out for in terms of good/bad quality meters? The ET44 is only $190, but I wonder why it is so much cheaper than anything else I see.
3) Finally, a four-point probe seems very cheap and easy to build and implement provided I already have a function generator and an oscilloscope. So why are most impedance analyzers so expensive? Would a DIY version be so inaccurate?

 

So why are most impedance analyzers so expensive? Would a DIY version be so inaccurate?

Hello there
impedance analyzers are the only instruments on the market with the measurement accuracy to evaluate components from µΩ to TΩ over the 20 Hz to 3 GHz frequency range, and to uncover the real characteristics of high-quality components. 0.65 percent basic accuracy and features accurate material measurement options that include temperature characteristics analysis from -55ºC to 150ºC and direct read function of permittivity and permeability,
measuring the density of electrolyte, Electrical impedance of biological tissue. Including measurements of... "You're going to like this"
(some liquid solutions and plaster samples).

 

Sorry to tell the good 30 USD impedance analyzer begins with 50 kHz and up (NanoVNA, ebay). So, not use for You.
But Ive solved that problem for case of milk cell impedance measure by INA-170, just apply it to measure resistor via what current is laid through the liquid cell, and to ease the measure cell - may use the two-electrode cell where polarity is cyclically changed (Patent of 1983 by Helmuts Maurops et al, ref SU1021440, see description at Espacenet or alternatively at SU/RU database). The simplest realization however too thermally instable was classical two multivibrators, one about 300 Hz and other 30 kHz for application in the milk cell, and microammeter between them to see the disbalance current. Yet there may be interest even more about BOTH components of current, active and separately reactive - then INA is only method to avoid 4 electrodes and keep accuracy and sensitivity high, and for sync with the signal phase probably CD567 or 4046 PLL tablet (You`ll need to separate the current phase off from voltage phase). Electrodes anyway must be from gold (or even better, platinum). Gold plated serves at milk for decades without polarization. By the way, both meanders must be supersymmetric, thus must be generated it by some 555 or more handy 4013 and then divide to 2 with other half of 4013 (RS/TT trigger). Russian 4013 (531/561 TM2) is readily generating but especially SMD versions if 4013 are very difficult to enstart - better add one transistor to them to alter K(u). However - Your case You need a freq sweep, thus may realize the both generators by ARM by means of soft (may begin with 328), so then ARM ADC will read the INA-170 and make a phase separation.

RE:"" when shopping for LCR meters"" - them are creating a massive electrode polarization what changes the value of impedance up to 100-fold. For example, typical result for milk would be 4-7 microSiemens per cm whilst by means of antipolarization pulsing circuit it jumps to 15-70 kOhm/cm.
RE:"ET44""- it is designed to take a reading at one single frequency for object where polarization is impossible. Thus, completely unuseable for any liquid cell.