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Discover our comprehensive range of Method for detecting pinholes in the latex gloves by use of Very High Voltage: PROFET

BACKGROUND

The fact that generated to Profet was the need for a faster and more efficient method of testing the medical examination gloves that could be easily integrated in an industrial production line.Currently, there are mainly two main methods for deciding whether or not a glove* is suitable for medical use. Both were slow and had other disadvantages also:

  • The Water Test: also known as the leak test, consists of filling the glove with a large amount of water (about 1 litter) and see if there are any leaks after two minutes. If there would be any holes, then small drops of water will leak through the material and, as a result, the glove would be considered to be pinholed ( inappropriate for use )

    • The method is very slow as it takes a few seconds to fill the glove ( about 10 seconds , so the glove won’t be broken by the water jet ) , more time for the glove to leak, another few seconds to empty the glove and so on . In the end , after about a minute, the decision can be made but it will result also a wet glove.

    • Besides the large amount of time it takes for the decision to be made, it is close to impossible to automate the whole process.

    • This test is usually a statistical one and it’s error margins are somewhat large.

  • The Brush Tes: It consists of detecting a current leakage through the pinhole by placing two electrodes over the two sides of the hole. Between the electrodes there a certain voltage which will produce a current (small discharge) through the hole and nothing will happen if the glove is not punctured. One electrode consists of a brush while the other one consists of conductive material that fill the glove.

Although this tests aredone automatically it had disadvantages:

  • The conductive material are hard to get out of the glove

  • The glove may come out contaminated after the test

  • The duration of the process faster than the Water Test yet isn’t fast enough

In order to overcome the disadvantages of the above tests, we developped the Profet, a highly effective apparatus that uses High Voltage to detect pinholes in the latex or synthetic gloves in a complete automated process.

The apparatus combines the benefits of a powerful Electrical field with the insulator properties of the materials, to make a difference between a good glove and a glove with a hole or pinhole

                      Description

Profet uses the force and penetration of a strong electric field to detect whether or not there are any holes in the surface of the latex glove.

The Profet consists of mainly of the following components:

· The Central Unit – Powering unit. It is used to convert the energy from the power supply into the electric field the apparatus uses. It has multiple buttons used to activate and control the apparatus and 4 main connections, situated on the back panel:

· The Main Electrical Plate: oval shape metal plate made of stainless steel. It connects to the Central Unit using a power cable that goes to the HV Output .The position of the Electrical Plate will vary as it will have to get in and out of the inflated latex gloves. The Main Electrical Plate represents the first electrode of the ensemble.

· The Sliding Sensor: A “U” shaped sensor that slides from one end of the glove to the other used to collect data. The sensor has two connections :

· As previously stated, the sensor is connected to the Reference Output, through a Contrast Resistor.

· The Sliding Sensor is directly connected to a Data Acquisition System / AtoD converter used to collect and format the data for the decision process.

· The Sensor consists of a very thin “Corona” type wire and represents the second electrode.

The U shape sensor is driven from one end of the glove to the other end by a step by step motor.

               Explaining and Modeling the Phenomenon

The Profet Generator, as stated, converts the energy from the power supply into the energy of a powerful electric field. Although it does not transform the electrical energy into a different form of energy, it generates the necessary signal to achieve our goal (detecting pinholes).

Mainly, it creates a high potential difference between the two electrodes:

Corresponding to this potential difference is the electrical field which can be calculated using Maxwell’s Equations and a derived formula would be:

The electric field vector equals the gradient of the potential function.

In order to understand the power of the electrical field, we will simplify as much as possible the equation of the electrical field by considering the following case: Let us presume that the potential generated by the Profet is continuous and constant and the two electrodes are two infinitely big plane metal plates.

Equation can be reduced to the following form:

- is the electrical field intensity vector

-potential difference between point a and b

-unitary direction vector from a to b , where a and b are two arbitrary points in space

The usual voltage value is about tens of KV and the distance is less then 10 cm. That means that the created electric field is about 10 KV / cm, enough to create a discharge through the air but not enough to discharge through the latex.

To continue with the explanation of the phenomenon, we shall analyze to process of measuring the glove.

  • The high potential difference is applied between the two electrodes.

  • Electrons start moving from the Positive electrode ( The Main Electrical Plate ) to the Negative Electrode ( the sensor ) driven by the created electrical field . Each electron is moved by the Coulombian Force :

e- electrical charge of the electron

  • Most of the electrons will have enough energy to reach the latex barrier but won’t have enough through it. However, a part of the electrical charge carriers will diffuse through the latex and , attracted by the Negative Electrode* will concentrate their directions to the sensor

  • Reaching the Corona wire, the electrons will form a small electrical current, which passing through the contrast resistor will create a small potential difference ( small as most of the energy was lost trying to pass through the latex ) .

  • Imagine now, that at a certain moment in time, the Corona wire and the Main Electrical Plate are perfectly centered on a pinhole. This time, most of the electrons won’t have to consume their energy to pass through the latex and as a result, they will reach the sensor in greater number. The resulting current will be higher and also the potential difference on the contrast resistor.

(5)

Therefore, the potential difference would be much higher if there would be a hole in the latex glove.

Modeling the phenomenon using the Resistor analogy For a better understanding of the phenomenon, we will start from the simple Ohm’s law.

Looking at the formula, it’s easy to understand that, having a constant potential difference and different resistor, we will have different values for the current. The greater the resistor value the lesser the current intensity.

Between any two points, we can calculate a resistance, whom value an be approximated with the following formula:

-resistance value

- resistivity of the material

- length of the region

A-surface of the region

The approximation is valid for the following case : the material has the same properties over all its axes ( this case : resistivity / conductivity ) , the considered surface is constant over all the length of the region. However, if the hypotheses are not true, the resistance can be calculated as a group of elementary resistors (can be calculated with (7) formula ).

By this manner, we can calculate the resistance between the two electrodes. As the material varies (air, latex, air) we have to calculate it as a series of 3 elementary resistors.

If A represents the Anode Electrode and B the Cathod then the 3 resistors are:

- resistance between the Anode and the glove

- resistance between the two side of the gloves

- resistance between the glove and the Cathod

Now that we have cleared the resistor analogy, think of the potential difference between the Anode and Cathod. It is applied over the equivalent resistor. In case of a pinhole there will be a decrease in the resistor value, therefore an increase of the current.

As shown in the picture below, the same potential difference will generate a greater current through a pinhole.

As stated n the description, the sensor will glide and collect data from all the surface of the glove. This is done in order to have a clear electrical image of the glove. The movement of the sensor is continuous, yet the data cannot be collected continuously. It is done in a discrete way. For the entire glove, we will collect a number of N values of current intensity*. [2]

This manner, we can consider the whole system as being a group of N resistor, and each one is measured separately, one at a time , corresponding to each sampling .

In the figure below, A represents the Main Electrical Plate and B the sensor. B moves from R1 to R4 ( or ­).

The sampling is done using a Data Acquisition Card. The electrical image of the glove will be the N values that the DAQ reads and records.

Mostly, if all the approximation we did by now would be true the decision process would be very simple (if the intensity value would be higher than the value for a good glove then we would have a pinhole ).

But there are a number of factors that lead us to a more complex decision process:

1. The potential difference is continuous but not constant. The signal applied to the Main Electrical Plate consists of many pulses like the one below:

2. The glove has not an uniform surface

3. The thickness of the glove is not uniform

4. The plate is not a perfect surface

5. The type of air is not constant

In order to decide whether a glove is punctured or not, the first step is to collect data. This means collecting a number of N values for each glove. After this is finished one of decision criteria can be applied

1. “Number of violations Criteria” :

· Before starting the decision process, some calibration good gloves are run through the Profet. Using the values for these gloves, the testing limits are calculated by the next method: for each measuring point, the maximum value of every good glove is considered to be a Threshold Value. This means evaluating the worst case Good Glove. After that the gloves are run through the apparatus. For each measuring point a higher value than the Threshold Value represents a violations. If a glove has more than a certain % of N (number of samples) then it is pinhole ,if not it is a good glove and will be used for the calculation of the new limits.

2. “Overall value” Criteria:· Uses a number of calibration gloves also. It sums the values of all the samples of a glove and the maximum result is considered the limit for the Good Gloves.· Then, the same is done for the tested gloves, using a simple rule. A higher value means a pinhole. To illustrate how the criteria are applied we have attached the results of a recent conducted test. The test consists of passing 15 gloves through the machine. The used gloves were 5 good gloves (used for calibration), 5 gloves with a pinhole in the palm and 5 gloves with a pinhole in one of the fingers (5 gloves each different finger). N, the number of samples, is 38, 19 samples for each sense. The sensor is moved by a motor, which makes a forward transition and 19 samples are collected, and after that a reverse transition and the other other 19 samples are collected.

We also ran an empty test (with no glove in the apparatus). All the data is a table below and for better understanding, the used abbreviations are:

  1. “Number of Violations” Criteria Result

For each glove with a pinhole we calculated the number of violations as follows: we took each sampled separately and compared it with the calculated limit (individually calculated for each and every sample number).We assigned one if the value was larger than the limit (meaning a violation) and zero if otherwise. After that we summed up the number of violations for each glove and the results are in the table below.

The number of violations for every good glove is 0 due to the manner of calculating the limits.

As shown in the table, for example, for the P1 glove, 31 one of the samples taken were larger than their corresponding limits and so on and so forth. As it can be observed it is very easy to decide whether the glove is punctured.

  1. “Overall Value” Criteria results

For this method we summed all the 38 samples for each glove and plotted the results in the bar graph. Value 1 is the overall value for the empty measurement, Values 3 to 7 are the overall values for the 5 good gloves, Values 10 to 14 are the overall values for the 5 gloves with a pinhole in the palm and Values 16 to 20 are the overall values for the 5 gloves with the pinhole in the fingers

To make a decission, we would only have to drag an horizontal line around 4000 and separte the graph as follows : the values above are bad gloves while the values below are good gloves
The Profet was developed for GURU reprocessing Tr@ce examination gloves. However the process is applicable to “on-line” manufacturing and is not dependent on the material neither the shape.

In the future it may be used to decide whether a material has the right texture and consistent thickness, integrity and/or if it meets all quality standards.

Daniel Bodea

R&D Director