FAQ - Active Models Hardware

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When questioning the working order of your Princeton Applied Research potentiostat/galvanostat, the first thing you should do is re-initialize the system (except for PARSTATs and VersaSTATs).  After that, you should perform some basic experiments with resistors, which we refer to as "Dummy cells".  Most Princeton Applied Research systems have an internal Dummy cell within the system (please refer to the User's Manual for your system for directions on how to switch from External to Dummy cell) so as rule out any problems with leads.  To test the system out to the leads, a resistor of known value that will allow proper testing of the system (sized such that the desired current and/or potential fall within the desired ranges) is also recommended.  To connect across a resistor, attach the Working lead (and the Sense lead if applicable to your system) to one side of the resistor and both the Reference and Counter leads to the other side of the resistor (with the Reference closest to the resistor).  This is what is referred to as a "Two-Terminal" connection.

With the system set to either the Internal Dummy cell or connected to an external resistor, apply a potential (or current in galvanostat mode) and determine if the corresponding current (or potential in galvanostat mode) is the expected value based on Ohm's Law.  For example, with a Princeton Applied Research 263A system set to its Internal DC dummy cell (a 10 kΩ resistor), an applied potential of 1 V should give a current reading of 100 µA (provided the current range is set to Auto or 100 µA) ± allowable tolerances.  Likewise for this same system, an applied current of 100 µA in galvanostatic mode across this 10 kΩ resistor should give a potential reading of 1 V ± allowable tolerances.  You may also run scanning techniques with the Dummy cell, each data point obeying Ohm's Law of E = IR.

If you feel that your system is not functioning properly with the Dummy cell, please contact the Technical Support department.  If the Dummy cell results appeared normal and your actual experiment is not giving the expected results, examine your setup carefully, giving special consideration to cell design, environmental interferences, bad reference electrode, bad connections, or grounding problems. 
An "E overload", or potential overload, can be one of either two conditions:
  1. The maximum input voltage (±10 V for most) of the differential electrometer has been exceeded.
  2. The compliance voltage (the maximum amount of voltage the power amplifier can provide across the working/counter interface) is at its maximum.
The E overload light will not distinguish between these two different conditions, so it is the responsibility of the user to determine which is the more likely cause.  One special note: if the leads are not connected to a cell, the voltage reading on the display of the system will "float" randomly and may report an E overload under these conditions.  This does not damage the system and occurs because there is an open loop in the differential electrometer circuit.  This would cease if you were to connect the working and reference electrode leads or connected a dummy cell across the leads.

An E overload due to exceeding the maximum input of the electrometer is usually seen when working with a low impedance cell (i.e. fuel cell or battery) in galvanic mode.

An E overload due to exceeding the maximum power amplifier output is usually a more serious condition because the full compliance voltage is being applied to the cell, causing possible damage to your electrode.  This condition is most often caused by a bad reference electrode or failure to connect the reference electrode.  Without a reference, the power amp continues to pump current into the system until it either overloads or reaches the desired potential (which it obviously cannot do without the reference in place).  Another common occurrence of this type of E overload is when working with highly resistive organic electrolytes.  Again, the power amp is pumping current trying to achieve the requested potential at the working electrode, but it must also overcome the iR drop between it and the working, which can consume many volts depending on the resistance and the distance.  To overcome this situation, reduce the distance between the counter and working electrodes.
An "I Overload", or current overload, is caused when the current flowing through the I/E converter exceeds the limit for a particular current range.  If you are getting a constant I Overload signal, try selecting either a higher current range or Auto Current Range mode.

If you are receiving an I Overload signal on the highest current range, it may be that your experimental design is in error (i.e. too large a sample or short circuit condition).  If you are performing an experiment in Auto Current Range mode, you will often see the I Overload (or "Ovl" or "Overload") light flash for a second as it approaches the limit for one current range, but extinguishes as it goes to the next highest current range.  This event does not affect the system or the data.  

In some instances, you may see the I Overload light flicker at a high frequency; this usually indicates some high frequency noise or highly capacitive cell is resulting in current spikes.  

Still another instance of an I Overload is when the system goes into oscillation, a condition which can be caused by a bad reference electrode, highly capacitive cell, bad connection at the leads, etc.  For more information on oscillations and noise, see the General section. 
Most of the Princeton Applied Research systems (PARSTATs, VersaStats, 263A, 283) can be configured into a ZRA.  In this configuration, no potential or current waveform is applied to the sample so this is considered an "open-circuit" technique.  For this special configuration, the electrochemical cell will be connected to the cable leads of the potentiostat is a different manner:
  • Working lead (green) is connected to one of the samples
  • If the Sense lead (grey) is available, connect it to the same sample as the working electrode
  • Ground lead (black) is connected to the other sample
  • Reference lead (white) is connected to the reference electrode
  • Counter lead (red) is not used
The configuration is used for such techniques as Galvanic Corrosion (current characteristics of two dissimilar metals immersed in a solution and measured as a function of time) or Electrochemical Noise (current and potential characteristics for two samples of the same composition measured as a function of time).  

Note:  Models 273 and 273A cannot be configured as an open-circuit ZRA in this manner.
You can check that your potentiostat is measuring the correct open circuit potential using a battery in series with the reference electrode.  To perform the test, assemble a cell and attach the potentiostat leads as shown in the figure below.  The reference electrode lead (RE) and the counter electrode lead (CE) are connected to one side of the battery and the sense lead (SE) and the working electrode lead (WE) are connected to the other side.  Note that some cables do not have the grey sense lead.  The black ground lead is not connected.  This should result in a stable OC measurement of about 1.5 - 1.6 V if the battery is fresh.  This value can be verified using either the Open Circuit or CV actions in VersaStudio, the Ecorr vs. Time technique within PowerCORR or the CV technique within PowerCV.  If you are using CV, make sure that your selected initial and final potentials are versus OC.


Princeton Applied Research 
Connection of the black ground lead on your Princeton Applied Research potentiostat/galvanostat is recommended for the following instances:
  1. The ground lead is connected to a Faraday shield surrounding your experimental setup, so that all environmental EMFs that strike the shield will be shunted to ground.
  2. If you have a PARSTAT, VersaSTAT, 283 or 263A system, the ground lead is also used for Galvanic Corrosion measurements to configure the system as a zero resistance ammeter (ZRA).
Thus, for the majority of applications, the ground lead should NOT be connected to anything.  Care should also be taken to avoid accidental contact of the ground lead to other metallic surfaces.  If you do connect it to something that is already at ground, you may actually be forming "ground loops" that introduce noise into your system.