Troubleshooting – Pine Research Instrumentation Store

This article is adapted from Section 8 of the User Manual for the Pine Modulated Speed Rotator (MSR).

This section describes some basic troubleshooting considerations when working with a rotator. Each of the basic problems is represented in a toggle below with suggested cause or action that should be taken. If problems with the rotator persist, contact the factory for further assistance (see Section 1.5).

No Rotation

If the rotator is not rotating, consider the following:

Confirm that the unit is connected to a live power outlet.
Confirm that the power switch has not tripped and that it is in the “on” position. Reset the switch if necessary.
Check the front panel circuit breaker and reset the breaker if necessary.
Check the motor control cable which connects the control unit to the motor unit. The connectors at both ends of this cable must be secured using the two screws on each connector.
The rotation rate knob may be set to full counterclockwise position. If this is the case, then rotate the knob clockwise to increase the rotation rate.
The motor, the shaft or one of the bearings may be frozen due to corrosion, or one of the boards or cables may be loose. Turn off the rotator, disconnect power, and then try the following procedure:

WARNING:

Risk of electric shock.
Disconnect all power before servicing the rotator.

AVERTISSEMENT:

Risque de décharge électrique.
Déconnectez toutes les sources d’alimentation avant de procéder à l’entretien du rotateur.

Check for freedom of rotation of the shaft by manually attempting to rotate the shaft.
Look inside the control unit and confirm that the printed circuit board is fully inserted into its connector.

Continuous Rotation at a High Rate

If the rotator is continuously rotating at a high rate, consider the following:

Check the motor control cable which connects the control unit to the motor unit. The connectors at both ends of this cable must be secured using the two screws on each connector.
Faulty connection or wire – contact the factory.
Faulty circuitry – contact the factory.

System Power Loss

If the rotator experiences a system power loss, consider the following:

The main power switch on the back panel is a circuit breaker which may trip and cause the system to lose power. To reset the breaker, turn the switch off and then turn the switch on again. Repeated tripping may indicate a more serious problem.

Front Panel Circuit Breaker Trips

If the front panel circuit breaker trips, consider the following:

This breaker only trips if the current passing through the motor windings is high enough to potentially damage the motor. This could occur if the electrode is spinning in a particularly viscous liquid, if the shaft is rubbing against something, or if an applied periodic waveform controlling the rotation rate has too great an amplitude or frequency.
This breaker (thermal type) is sized to limit the average motor current to within the motor specification. Running the motor at a high modulation frequency, or with large amplitude changes, or a combination of the two, may cause tripping. It may be necessary to reduce the modulation frequency and/or amplitude to prevent tripping of the breaker.

Rotator Spins Backward

If the rotator is spinning backward, consider the following:

When the rotation rate knob is in the full counterclockwise position, it is natural to expect that the rotation rate should be exactly zero. However, it is normal for there to be a small residual rotation rate, and often this is in the reverse direction.
If a negative voltage signal is applied to the INPUT jacks on the front panel of the control unit, then the rotator will spin backwards. If this is undesirable, reverse the polarity of the signal applied to the INPUT jacks.

Excessive Audible Noise

If the rotator is excessively loud, consider the following:

If the rotator has a standard lower bearing assembly with a stainless steel bearing, then this bearing may be corroded. If corroded, replace the entire lower bearing assembly.
Internal spindle bearings are worn – contact the factory.

Electrical Noise in Voltammograms

Electrical noise in voltammograms can be caused by a number of factors. Broadly, these factors are categorized as environmental, grounding issues, brush wear, and cell connections. They are discussed separately below.

Environmental

Environmental electrical noise can be solved by checking the following:

Make sure that working, reference, and counter electrode cables do not cross or travel near power cords, video cables, or network lines.
Make sure that the potentiostat and rotator are located as far as possible from hotplates, ovens, video monitors, computers, network hubs, wireless devices, or cellular telephones.

Grounding Issues

Electrical noise caused by grounding issues can be solved by referencing Section 4.5 and by checking the following:

Confirm that the earth ground connection on the rotator is connected to the chassis ground of the potentiostat.
Confirm that all metal objects (such as cell clamps and ring stands) near the electrochemical cell are connected to the earth ground connection on the rotator.
Confirm that all grounding connections are made to a common grounding point to avoid the formation of “grounding loops”. Note that grounding loops are sometimes non-obvious, especially when multiple instruments and computers are connected together.

Brush Wear

Electrical noise caused by brush wear can be resolved by doing the following:

Always use a banana jumper cable to connect opposing brushes together. Two brushes in opposing contact provide a better electrical connection.
Inspect all brush contacts. Brushes should have a concave groove worn in them which exactly mates with the rotating shaft. The depth of this concave groove naturally increases over the lifetime of the brush. A new brush should be worn continuously for approximately eight hours to intentionally wear a groove into the brush to increase the surface area of the brush that is in contact with the shaft.

Cell Connections

Electrical noise caused by cell connection issues can be resolved by doing the following:

Confirm that the reference electrode has low impedance and is in good contact with the main test solution. High impedance at the reference electrode is often caused by a plugged frit, which impedes current between the inner chamber of the reference electrode and the main test solution. High impedance may also be encountered when working with low dielectric media (such as non-aqueous solvents).
Use working, reference, and counter electrode cables which are shielded (coaxial) cables.
Confirm that any alligator clips being used for connection to the electrodes are not corroded and are securely fastened to the electrodes.
Note that many potentiostats utilize a driven shield to protect the reference electrode signal. This driven shield is connected to the outer shield line in the coaxial reference electrode cable. Only the inner signal line of the coaxial cable should be connected to the reference electrode. The outer shield line should not be connected to anything at the cell end of the cable. Do not ground such a driven shield line as it may cause the potentiostat to oscillate or malfunction.