The present invention is a passive data logging device for logging exposure of an article to one or more environmental conditions such as high or low levels of temperature, pressure, humidity or light.

There is a known need to monitor the exposure to certain conditions, such as temperature of an article, over an extended period of time and provide data to a user. Such data can potentially enhance a wide range of logistics management activities. For example, the service lifetime of an article with a specified shelf life could be extended if it is possible to make informed decisions based on measured exposure to temperature over lifetime rather than arbitrarily withdrawing all items from service at a fixed time based on worst case exposure scenarios.

Attempts have been made to produce passive devices that are low cost and yet which provide the necessary temperature data. For example, one known temperature logging device comprises a fluid reservoir and one or more channels and is designed to be triggered manually by opening the barrier between two reservoirs and then letting the fluid flow through the channels at a rate governed by the temperature of the device. However, such devices usually require the use of very specific liquids, are inaccurate, and cannot be adapted easily to work over differing temperature ranges. Furthermore, it can be difficult to get them to work over longer time periods.

Accordingly, there is a need for a low cost data logging device which is accurate, simple to manufacture from relatively low cost materials, and which can work over extended time periods and in particular data ranges. According to the present invention there is provided a data logging device comprising: a fluid reservoir containing a fluid; a porous media through which the fluid can pass; a valve connecting the reservoir and the porous media and controlling flow there between; and an actuator configured to actuate the valve when the device crosses a predetermined applied parameter threshold so that the fluid can flow from the reservoir along the porous media; such that the article is arranged to provide, in use, an indication of the progress of the fluid through the porous media to indicate the total time that was spent by the device past the predetermined parameter threshold.

The device of the present invention can be formed as a small, low profile and flexible card that can be attached to a wide variety of equipment to allow long- term (e.g. 5 years) logging of exposure to the particular parameter. The device has the ability to capture a histogram-style output, showing a detailed picture of the time the equipment has spent within a particular range over its lifetime.

The invention makes use of capillary flow of fluid from a reservoir into a porous media, which forms the logging function. The valve controls the connection between the fluid flowing from the reservoir into the porous media and is actuated by an actuation mechanism that is passively dependent on the parameter being detected to ensure that the fluid flow and thus the logging is only active between the given parameter range.

The present invention also provides an array of devices of the type defined above whereby each valve is actuated at incremental parameter intervals so that the array forms a histogram style output of the time spent at certain intervals of parameters.

The invention may also be configured to provide logging only when a specified parameter is outside a specified maximum and minimum range.

The actuator may be dependent on one or more of temperature, humidity, pressure, or UV exposure. The porous media across which the fluid is drawn may be tuned to compensate for the changes in the fluid rheology affecting fluid flow that are a function of temperature changes. Examples of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a cutaway view of a device according to the invention;

Figure 2 is a top level view of the device of Figure 1 ;

Figure 3 is a view of an array of devices according to the invention;

Figure 4 is a view of a further example device according to the invention;

Figure 5 is a view of a further example device according to the invention;

Figure 6 is a cutaway view of the device of Figure 5; and

Figure 7 is a top level view of a further example device according to the invention.

An example device 10 according to the invention is shown in Figure 1 , which shows a cutaway of the main components of the device 10. A fluid-filled reservoir 7 has an entry port 1 connected to a valve 2. The reservoir 7 may be formed as a channel. The port 1 acts as an interface between the valve 2 and a porous logging media 3. The valve 2 is actuated by an actuator 6 which can be a shape memory alloy or a bimetal strip for temperature logging, or a pressure- sensitive actuator for pressure logging, for example. When the device 10 is within the correct parameter range the valve 2 is actuated by actuator 6 to align the output port 5 of the valve 2 such that the fluid is in contact with the porous media 3. When the article is outside of the parameter range, the actuator 6 will move the valve port 5 up or down such that the fluid is no longer in contact with the porous media 3 but is in contact with either a separate porous media designed to hold the fluid or just in contact with a surface.

Figure 2 is a top level view of the device 10 of Figure 1 showing a viewing window 4 which allows viewing of the logging media 3 and shows the fluid path from the reservoir access port 1 to the reservoir channel 7 which runs along the valve 2 itself.

An example implementation of a combined array 12 of devices 10 according to the invention is shown in Figure 3 which allows for the monitoring of temperature. A number of devices 10 that are active over different ranges allow for a histogram output of the history of the logged parameter (e.g. temperature). A further example device 67 according to the invention is shown in Figure 5, which shows a cutaway of the main components of the device 67. A reservoir 63 made of a porous material is filled with logging fluid, which upon direct contact with a given porous media 3 allows fluid to flow from the reservoir 63 to that porous media 3. The flow of fluid from the reservoir 63 to the porous media 3 does not occur when the reservoir 63 is not in contact with the porous media 3. In this instance the valve action is provided by the reservoir 63 engaging and disengaging the porous media 3. The reservoir 63 is actuated as a function of the logged parameter. In the example device the actuator is a bimetallic coil 64 which actuates according to temperature. Alternative actuators could include shape memory alloy for temperature logging, or a pressure-sensitive actuator for pressure logging, for example. In the example device, the actuator 64 is fixed via a pin 65 to a solid housing 66 such that the actuator 64 moves with respect to the housing 66 as the parameter changes. The array 68 consists of a porous media 3 arranged on a flexible substrate 61 such that each porous media 3 indicates a specified upper and lower parameter range such that as that parameter changes, the reservoir 63 comes into contact with the specific porous media 3 whose upper and lower parameter range bounds the current parameter value.

A cross section of device 67 is shown in Figure 6 which shows an implementation in which a layer 68 joins the porous media 3 and solid housing 66 to the flexible substrate 61. In this instance, the reservoir 63 is shaped such that the friction between the reservoir 63 and the porous media 3 may be reduced such that the area contacting the porous media 3 is small such that the reservoir 63 contacts the porous media at a defined location. In the implementation wherein the actuator 64 is a bimetallic coil the contact force between the reservoir 63 and the porous media 3 may be provided by the spring force of the coil.

Where the reservoir 63 and valve is a single porous material, the pore size of the reservoir must be greater than that of the porous media 3 to enable the fluid to flow from the reservoir to the porous media 3. The difference in pore sizes between the reservoir 63 and porous media 3 must also be sufficient such that the rate at which fluid transfers from the reservoir 63 to the porous media 3 is minimally dependent on the volume of fluid remaining within the reservoir 63. Another example device 72 according to the invention is shown in Figure 7, which shows a top down view of the main components of the device 72. In this instance, the reservoir 63 comprising a porous nib is situated in the middle of an extended arm 74 of the bimetallic coil 64. In this implementation, the reservoir 63 is suspended above the substrate 61 such that there is no friction between the two. The free end of the arm 74 is placed between two stoppers which provide a means of providing a resistive force to the arm 74 when actuated by the entirety of the actuator 71 such that erroneous contact between the reservoir 63 and porous media 3 due to vibration is reduced. In this instance, the porous media 3 are oriented such that they are perpendicular to the plane of the substrate 61 such that the suspended reservoir 63 contacts a specific strip when the device 72 is at a maximum or minimum temperature threshold. Consequently, logging fluid is only transferred to the porous media 3 when the device 72 is at these thresholds and the device 72 logs the duration spent at or exceeding these thresholds.

The fluid reservoir should have a small enough radius or average pore size such that the required volume of fluid is held in place by surface tension. Also, there should be a suitable exit to atmosphere to allow the fluid to flow through the porous media 3. Likewise, the logging media 3 must have a suitable exit to the atmosphere to avoid pressure build up. The fluid flow into a porous media or plurality of capillary tubes forms the logging mechanism. To achieve significant logging times, it is desirable to have a highly viscous fluid and a porous media which has a very fine pore radius. Furthermore, to ensure that the flow of the viscous fluid is independent of the orientation of the device with respect to gravity, the surface tension is preferably small and the radius and density of the fluid small also. A suitable example of a logging fluid is a silicone oil. By tuning the viscosity and pore radius, it is possible to achieve different logging time periods and accuracies making the invention suitable for a variety of different time periods, from hours to many years. The above example provides a visual indication of the data that is recorded. However, electrical readout is possible to increase the accuracy of the readout. In such a case the fluid, such as silicone oil can be used to alter the electrical properties of a circuit (such as an RFID tag) that can be interrogated to determine the distance that the fluid has travelled along the porous media 3, and thus the total time spent in a temperature band.

The porous media may vary in structure across its length so that the amount of wicking of the liquid in the porous media varies over time or over different parameter ranges. By use of a variable structure it is then possible to control the nature of the indication of the amount of exposure of the device to a particular parameter or to provide different indications dependent upon the amount of exposure to different parameter ranges over different periods of time.

Any fluid will have some temperature dependence of its rheology. This can significantly affect the accuracy of the logging mechanism. When the invention is for the logging of temperature, this is controlled by the valve which ensures that the device will only be logging over a narrow range of temperatures. For the logging of parameters other than temperatures, then to solve the problem of rheology temperature dependence, the porous media 3 can be designed to also react to the change in temperature to compensate for the change in fluid rheology. The porous media 3 can be formed from a plurality of channels over which a fluid will wick. The actuator 6 can be selected to actuate the valve 2 by being capable of responding to an environmental stimulus which will allow the fluid to flow by capillary action from the reservoir 7 along the porous media 3. With an array of devices 10, each designed to act over a different environmental parameter range, a histogram style output of time vs. environmental parameter can be gathered. The device 10 or array 12 of devices can then act as a passive environmental data logger, for example it can act by recording the total time that a device spends within different intervals of environmental parameters (such as temperature, humidity, pressure, UV exposure). This output allows, taking the example of temperature, a histogram indicating the time spent within a range of temperatures, for example. 2 weeks spent within 20 - 25°C, and 1 month between 25°C - 30°C. As mentioned above, the device may be configured to monitor one of a number of environmental parameters. For humidity monitoring the bimetal coil of the examples above can be replaced with a device capable of producing a rotary motion dependent upon the humidity (e.g. goldbeater's skin - which has hygroscopic property, and is used as the sensitive element in hygrometers where variations in atmospheric humidity cause skin contraction or expansion);

For pressure monitoring a change in air pressure could be used to cause a rotary motion in a fashion similar to that for humidity detection. For UV exposure the device can use a radiometer capable of converting light into a mechanical motion (e.g. a Crookes radiometer).

It will be appreciated that the present invention has a number of advantages when compared to prior art configurations. Firstly, it is low cost, the data logger can be manufactured from a moulding or layer based manufacturing process using simple materials. Secondly, it can be configured to be easily read without any special equipment. Furthermore, the device can be pre-printed or marked with levels specific to an article or piece of equipment to make it clear when the equipment has gone outside of its temperature limitations. It is also simple to deploy, the device can be deployed by sticking it on a desired equipment or temperature sensing target.

The device 1 can also have a means to initiate the logging. One possible implementation is shown in Figure 4, which includes a simple activation member, provided by a strip 7 which mechanically fixes the valve 2 into an off position until its removal. After removal, the valve 2 is free to move and operates as previously described. For an array of devices 1 , this could still be a single strip common to all elements. As mentioned above, the device is able to log data over long time spans. For example, a small credit card shaped device can log data at 5 degree intervals from -10 to 100°C for 1 year. It is also accurate, the logging accuracy is more than suitable to make decisions regarding the life cycle of a product. For example, a month's worth of logging would have a temporal error of around 12 hours. The relative error over a year's logging range has been estimated to be as small as 4% (which is -14 days).

The device has application in a number of fields. One is defence where data can potentially enhance a wide range of logistics management activities, e.g. the service lifetime of kit with a specified shelf life could be extended if it is possible to make informed decisions based on measured exposure to temperature over lifetime rather than arbitrarily withdrawing all items from service at a fixed time based on worst case exposure scenarios.

Another is medicine where a built in device can remove some of the burden of more sophisticated cold chain management systems, and also acts as a final guarantee to the end user of the supplies who can be assured of their condition since delivery

Certain high end food and drink items (e.g., wine) can benefit from an integrated temperature log within the packaging to act as a guarantee to the environment they were stored within. Also, the incorporation of such a low cost device into generic cold chain packaging is of interest to packaging suppliers for reducing the cost of traditional environmental monitoring or to offer an additional guarantee to customers. Various situations require long term environmental monitoring, and the low cost nature of such a device means that the temperature environment can be carefully observed. An example might include antiques or artwork in galleries. Another example use is in the insurance industry where insurance companies can require some sort of evidence that goods were or were not taken outside of a designated temperature range.