A tape-drive condensation sensor includes a probe with first and second spaced-apart electrodes that define a passage for air flow within a pneumatic conduit. A voltage source is coupled between the electrodes and the voltage of the source and the spacing between the electrodes are adapted to pass a current when a drop of condensation forms between the electrodes. An alarm circuit is activated by the flow of current, the alarm being adapted to signal an event of discernible condensation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to condensation sensors and, in particular, to a sensor for a tape-drive device in a computer library system.

2. Description of the Related Art

It is often a problem that atmospheric water vapor condenses on mechanical or electrical equipment causing corrosion of metal parts. This can occur when air that contains water vapor comes into contact with metal structures that are at a relatively low temperature. Accordingly, equipment exposed to changes in temperature, as well as changes in air pressure, can degrade and ultimately fail as a result of unwanted condensation.

In large computer systems, data storage is often provided by means of cartridges and tape drives. These devices are used within an environment of controlled temperature and humidity to decrease the potential for performance degradation and failure due to corrosion. However, the systems that control temperature and humidity are themselves subject to failure; therefore, it is desirable in critical computer systems to provide some form of backup humidity-sensing capability.

Devices capable of sensing the presence of condensation are known in the art. A typical prior-art sensor, including an alarm, is illustrated in FIG.1. Such a device20consists of a condensation sensor22and an alarm circuit24. The sensor22typically comprises thin conductive strips26A,26B attached to an insulator surface28and positioned so as to define a gap30therebetween. The thickness of the conductive strips26A,26B is shown greatly exaggerated inFIG. 1for the purpose of illustrating the structure of the sensor22, but in a typical prior-art sensor their thickness is arbitrary and plays no appreciable role in the operation of the sensor, so long as a gap is created between them for receiving condensation formed in the environment around the sensor.

It is ordinarily desirable to construct the sensor22as small and as thin as possible, so as to not interfere with other structures in close proximity to the sensor. In operation, a first voltage is applied to the conductive strip26A and a second voltage to the conductive strip26B, thereby creating a potential difference between them. As a result, if sufficient moisture condenses to fill the gap30between the conductive strips26A and26B, a current flow is established between them. The alarm circuit24is adapted to respond to the current by setting off an alarm. The sensor20may be attached to any surface where moisture is undesirable.

While the prior-art sensor22ofFIG. 1is generally satisfactory for its intended purpose, several problems with its performance limit the scope of its usefulness. The first problem is that the alarm is set off only after the onset of condensation on the surface of the sensor. Therefore, when the alarm is triggered, condensation may already have occurred at other sensitive parts of the device being protected. Moisture can condense on a surface of interest in a device, such as the head of a drive, before it condenses on the sensor22if that device is colder than the sensor. Similarly, moisture can condense on another surface at the same time as it condenses on the sensor22if the two surfaces are at the same temperature. In either case, the condensation sensor20of the prior art at best provides a simultaneous indicator of condensation, which may not be sufficient to properly protect the device by avoiding condensation altogether.

This problem is particularly problematic in the context of tape drives and libraries in large computer systems, such as mainframe computers, that are sensitive to all environmental conditions. Accordingly, these systems are normally situated in computer rooms with environmental-control systems whereby temperature and humidity can be set and maintained precisely. However, as a result of human error or of malfunction of the control systems, environmental conditions that produce condensation on tape drives and other sensitive components can and often do still occur.

In theory, once a condensation sensor of the type shown inFIG. 1detects moisture and the alarm is set off, the environmental system can be adjusted to prevent condensation. However, by the time the alarm is set off, condensation is likely to have already occurred on surfaces that are at the same temperature of or colder than the sensor, as mentioned above. In addition, further condensation continues to form until the environmental conditions have actually changed to safe levels. This lag time can be significant, especially if the adjustment of environmental parameters is performed manually by an operator who may be slow to respond to a warning because of inadvertence or error.

Moreover, even after the environmental conditions have changed, it may take considerable additional time before the moisture that has already condensed actually evaporates. When the air temperature is only a few degrees above the dew point (that is, when the air is only slightly less humid than at saturation), the rate of evaporation is very slow. Thus, another limitation of prior-art sensors is that condensation can remain on sensitive surfaces for significant periods of time after detection within a protected environment. Since the presence of even small amounts of moisture for limited time periods can be undesirable, this is a significant disadvantage.

A second problem with prior-art sensors of the type illustrated inFIG. 1in the context of tape-drive protection is that for best results the sensor needs to be mounted on or near the head of the tape drive. This may not always be possible because tape drives are complex mechanisms with many components and, at the very least, the process of adding a sensor complicates the design of the drive. Therefore, condensation sensors are typically installed on stationary structures in the vicinity of the protected device, often at a sight that may or may not reflect the environmental conditions of the device of interest.

Accordingly, there is still a need for a condensation sensor that is capable of detecting when the environment of a protected device approaches the conditions required for condensation of air moisture, so that a warning in advance of the actual onset of condensation can be provided. In addition, there is a need for a condensation sensor that can detect the potential for condensation at the sight of a device of interest without having to be mounted on the device itself.

BRIEF SUMMARY OF THE INVENTION

An objective of the invention is a sensor that detects the potential for condensation on a device at the onset of the conditions leading to condensation, preferably prior to the actual formation of water droplets on the device.

Another objective is a sensor that is particularly suitable for anticipating and preventing condensation on devices that utilize pneumatic control systems, such as tape drives.

A final objective is a condensation sensor that can be adapted for use on a variety of devices without requiring any change to the design of the device of interest.

According to these and other objectives, the present invention consists of a probe that includes first and second spaced-apart electrodes that define a passage for air flow. A voltage source is coupled between the electrodes, and the voltage and the spacing between the electrodes are adapted to pass a current from one of the electrodes to the other through a drop of condensation formed in a gap therebetween. An alarm circuit is activated by the flow of current and is adapted to signal such an event of discernible condensation to an operator or an automated environmental-control system.

The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings and claims. However, such drawings, description and claims disclose only some of the various ways in which the invention may be practiced.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

This invention is based on the realization that several advantages can be obtained by placing a condensation sensor within an airflow stream in the vicinity of a protected device. As a result, the onset of condensation is more likely to be detected prior to actual formation of water droplets on the device.

Referring to the drawings, wherein like parts are designated throughout with like numerals and symbols,FIGS. 2 and 3illustrate a condensation sensor in accordance with the present invention and generally designated by reference numeral50. The condensation sensor50includes an alarm circuit54and a probe52mounted within an air conduit60. The probe52is shown as including three pairs of electrodes56A,56B, but it could equivalently include more or fewer pairs. The electrodes may have rounded or flat sides and are positioned in spaced-apart configuration, so that each pair defines a passage62for airflow in either direction within the conduit60. Preferably, each electrode consists of a segment of conventional wire mounted between opposing non-conductive support plates63. Each pair of electrodes is preferably spaced apart no more than 1 mm, optimally about 0.1-0.3 mm.

As shown inFIG. 2, the alarm circuit54includes a voltage source64and an alarm indicator, such as an LED66. A first terminal68of the alarm circuit54is coupled to each of the electrodes56A and a second terminal69is coupled to each of the opposite electrodes56B.

In operation, the voltage source64establishes a voltage potential difference between each pair of electrodes56A,56B. Accordingly, if a drop of water W condenses between any of the electrode pairs, as illustrated inFIG. 3, a current is passed from one electrode to the other and causes the LED66to light. Thus, the LED serves as an alarm signal. As one skilled in the art would readily recognize, alarm circuits providing different forms of signaling may be equivalently employed as desired. For example, the alarm circuit may be adapted to provide an audible signal or an iconic symbol on a computer monitor, or may provide an input to a computer program or to an automatic control device.

The electrodes56A and B are preferably positioned vertically and in parallel, so as to increase the chance of accumulation of condensation at the bottom of each pair of wires. That notwithstanding, because of the screen effect provided by the plurality of wires positioned across the section of the conduit60, droplets of water may form anywhere between two electrodes and immediately trigger the alarm. Therefore, this embodiment of the invention is preferred.

Turning now toFIGS. 4 and 5, an alternative embodiment of a condensation sensor and alarm unit in accordance with the invention is illustrated, and generally designated by reference numeral70. The unit70includes a probe72and a alarm circuit74. The probe72is mounted within an air conduit60and includes a pair of electrodes76A,76B formed in arc shape to conform to the interior of the air conduit. The electrodes76A,76B define a passage78for airflow and are spaced apart to form a gap80for collection of water condensation. If water drops form as the result of condensation anywhere along the span of the electrodes76A,76B, gravity causes them to flow toward the gap80. If sufficient condensation forms to fill the gap, the probe72becomes electrically coupled to the alarm circuit74to activate an alarm, which operates in the same manner as described above with reference to the previous embodiment of the invention. The gap80is preferably no more than 1 mm wide.

Referring toFIG. 6, a partial view of an IBM 3590 tape drive90is illustrated, including a pneumatic pump92that provides vacuum and pressure to the drive through air conduits94. As shown in the portion of the figure referenced as detail A, a condensation sensor50according to the invention may be advantageously mounted in one of the conduits94, preferably on the pressure side of the system. In the typical operation of a tape drive, a cartridge enclosing a reel of magnetic tape is inserted into the drive and an arm engages the end of the magnetic tape. The magnetic tape is pulled from the tape cartridge, threaded around various rollers, and spooled onto a take-up reel. The path that the magnetic tape takes brings it adjacent to, or in contact with, a head used to read the magnetic tape. The tape drive causes the magnetic tape to travel back and forth across the head to desired read points. Thus, the tape is placed under high tension variations by the tape drive to accommodate high speed tape movement and abrupt stops.

In order to minimize friction along the tape path which produces wear and, ultimately, could cause the failure of the magnetic tape, pressurized air is directed through the air conduit94toward the magnetic tape at points where tape contact with the surface is not desired. For example, pressurized air is typically used to provide an air bearing between the magnetic tape and the magnetic tape head. Typically, the air provided in the conduit is also of a controlled humidity and temperature in order to reduce or eliminate the formation of condensation on tape-drive surfaces over which the air passes.

While the condensation sensor and alarm of the invention may be attached to any surface, it is advantageous to install the probe within the interior of the air conduit94. The invention is in part based on the recognition that a condensation sensor is more effective within an air conduit because flowing air is necessarily at a higher pressure than outside the conduit. Since the dew point of air increases with pressure (all else being equal), condensation will occur at a slightly higher temperature in air flowing in the conduit. Therefore, the probe52(FIG. 2) is likely to detect the onset of condensation prior to actual formation of water droplets downstream of the conduit, where the air is prevalently stationary and at a lower pressure.

Moreover, the configuration of the probe52(FIG.2), which allows air to flow between pairs of electrodes, is particularly advantageous in this environment because its thin-wire structure presents a minimal surface to obstruct air flow. Therefore, the probe produces negligible back pressure or other interference in the operation of the pneumatic system of the tape drive. The probe72of the second embodiment of the invention (FIG. 4) is similarly suitable for installation in a cylindrical conduit because it does not materially affect the overall geometry or functioning of the system. Because of the relatively large area and the sloped configuration of the electrodes76A and B, the accumulation of condensation at the bottom of the conduit is favored.

The terms and expressions that have been employed in the foregoing specification are used as terms of description and not of limitation, and are not intended to exclude equivalents of the features shown and described, or of portions thereof. Accordingly, the scope of the invention is intended to be defined and limited only by the claims that follow.