Saturated current probe

Besides these potentiometric sensors there are also amperometric sensors using the principle of ion conductive solid electrolytes. In addition to the heating voltage those sensors are also equipped with a second voltage supply, inducing a current, which varies depending on the concentration of the test gas. Fig. 3.19 shows a schematic view of these so-called saturating current probe. 

When a probe is inserted into a plasma, it will experience electrons and ions colliding with its tip. Due to the high mean speed of electrons, the flow of electrons is higher than the flow of ions. Consequently, the tip will charge up negatively until the electrons are repelled, and the net current then is zero. The probe potential then is the floating potential, Vfl. The electron current density Je then balances the ion current density 7,. At potentials lower than Vfl the ion current cannot increase further—in fact, only ions are collected from the plasma—and the ion saturation current /,s is measured. The plasma potential Vpi is defined as the potential at which all electrons arriving near the probe are collected and the probe current equals the electron current. Note that the plasma assumes the plasma potential in the absence of a probe hence probe perturbation at Vpi is... 

Current transformers used in transient current measurements must have a peak current rating at least equal to the maximum expected currents otherwise, current peaks are lost in the data due to saturation of the current probe. Figure 9.6 indicates how current probe saturation resulted in a flat-top current waveform and loss of vital information, making power quality analysis more difficult. 

In this method, two saturated calomel reference electrodes (SCEs) are used as the potential probes, Pt gauze is used for both current probes, and 1 M H2S04 is the electrolyte. Figure 5.14 shows the schematic of the hardware and instruments in this method. 

Also presented in Table I are temperatures of the flame as measured by others ( 16, 17) and the saturation currents measured by Frier. With the assumption that no colhsions between positive ions and neutral gas molecues occur within the ionic sheaths surrounding the probe wires (vahd here because the mean free path of the species considered is larger than the thickness of the sheath), the relation between the saturation current and the ionic concentration is ... 

Ensure this current probe in particular, does not saturate (because the operating supply current also adds to the flux in this)... 

The above equation allows the heat transfer to be described when chemical equilibrium is established. Note that when Le = 1 Eq. (33) airi (34) are the same. This analysis, proposed by Pfender has been verified using some experimental results which show that the frozen boundary layer hypothesis is correct. The measurements have b n performed in a free burning argon arc with different water cooled probes, (cp < 0.5 mm). The influence of the charged particles has been determined by the measurements of the saturation current in the probe maintained at a floating potential. 

In addition to their use as reference electrodes in routine potentiometric measurements, electrodes of the second kind with a saturated KC1 (or, in some cases, with sodium chloride or, preferentially, formate) solution as electrolyte have important applications as potential probes. If an electric current passes through the electrolyte solution or the two electrolyte solutions are separated by an electrochemical membrane (see Section 6.1), then it becomes important to determine the electrical potential difference between two points in the solution (e.g. between the solution on both sides of the membrane). Two silver chloride or saturated calomel electrodes are placed in the test system so that the tips of the liquid bridges lie at the required points in the system. The value of the electrical potential difference between the two points is equal to that between the two probes. Similar potential probes on a microscale are used in electrophysiology (the tips of the salt bridges are usually several micrometres in size). They are termed micropipettes (Fig. 3.8D.)... 

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