Abstract:
The subject of the invention is a coating thickness gauge with at least one measuring probe ( 14 ) which has at least one sensor ( 15, 15 ′) as well as a device for the zero adjustment and/or calibration. The coating thickness device ( 10 ) is equipped with means to automatically activate zero adjustment and/or calibration when an interaction especially a contact or a relative movement between a sensor ( 15, 15 ′) and a reference plate ( 11, 11 ′).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a gauge to measure a coating thickness with at least one probe, that has at least one sensor as well as a device to make the zero adjustment and/or the calibration. 
     2. Description of the Related Art 
     All gauges on the market to measure a coating thickness require a regular check of the zero adjustment and, if necessary, of the calibration. This has several reasons. Either the gauges were out of use for a longer period of time, batteries had to be exchanged, or measuring conditions considerably vary from normal conditions due to extreme environmental temperature fluctuation, changes to kind or thickness of substrate, the gauge or the probe themselves. As a rule, even the exchange of the probe requires a new zero adjustment or calibration. To do so, prior to taking a measurement the gauges or the probes have to be placed on a reference plate and the zero adjustment or calibration has to be started by pressing the operation button. This procedure is, for example, described in patent DE 34 04 720. 
     U.S. Pat. No. 5,293,132 also states a method for zero adjustment, where the user has to decide on which substrate a measurement will be taken in order to, if necessary, manually switch the gauge in case of a change of material. In case of a material change the user is requested by the device to make a zero adjustment. The user is compelled by the described device to do the zero adjustment, as otherwise no measurement can be taken. With other known devices there is the danger that with omitted adjustment of the device the measuring results are falsified. By no means, the device has integrated reference plates so that via control elements the device has to be informed about the type of reference plate in use during manual adjusting. This may cause confusion. 
     A further disadvantage of the previous gauges is that the zero adjustment and positioning depends on how it is performed. The placing of the probe at different spots or uneasy placing may possibly cause very different results. This does not only lead to inaccuracy but also makes it difficult to compare measuring results of measuring gauges that usually have comparable characteristics. 
     Furthermore, devices to measure a coating thickness with separate probes are known, that are either connected with the device via a cable or data are wirelessly transferred to the measuring gauge. The probes are designed in a way that the taking of measurements starts upon placing them on the surface to be tested. But control elements are still necessary to do the zero adjustment or calibration. The adjustment or calibration on reference plates has to be started and realized individually by the user. 
     SUMMARY OF THE INVENTION 
     It is the task of the invention in question to propose a coating thickness measuring device that avoids the usual difficulties and error sources that are resulting from zero adjustment and calibration necessary for the known measuring gauges. 
     This task is solved by the device in accordance with the invention by providing the coating thickness measuring device with means that in case of interaction, especially in case of contact or a relative movement between a sensor and a reference plate, automatically activate the zero adjustment or calibration. Especially, the advantage of this device is that the user of the device always gets a correct adjustment made under the same conditions. Thus the adjustment is not subjected to individual influences. 
     Preferred versions of the invention are defined by the sub-claims. 
     For example, a device with a removable probe unit in accordance with a preferred version is proposed, that upon having been taken out automatically performs the zero-adjustment thus the measurement can be taken immediately. 
     Moreover, the coating thickness measuring device in accordance with the invention can have integrated reference plates. Advantageously, when placing the probe the device recognizes on which reference plate the zero-adjustment or calibration shall be made and automatically carries it out without control elements being actuated by the user. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is described by means of preferred versions with reference to enclosed illustrations as follows: 
     FIG. 1 a principle description of a coating thickness measuring device in accordance with the invention; 
     FIG. 2 a preferred version of a coating thickness measuring device in accordance with the invention with a fixture for the probe; 
     FIG. 3 a principle illustration of a probe unit for a coating thickness measuring device with a micro processor; and 
     FIG. 4 a principle illustration of a coating thickness measuring device with a micro processor interacting with the probe unit. 
    
    
     FIG. 1 shows the principle illustration of a coating thickness measuring device in accordance with the invention. The device  10  is connected with one or more reference plates  11 , 11 ′, to which a switch respectively a sensor  12  is connected that records the placing of a measuring probe. The measuring probes  14  are zeroed on the uncoated reference plates and are calibrated on the plates with a known coating thickness. A signal, depending on whether there is a zero reference plate or a calibration plate, will be sent to the coating thickness measuring device  10  and a zero adjustment or calibration will be started automatically. After that the measuring probe  14  is adjusted and measurements can be taken. Advantageously, these reference plates  11 , 11 ′ are integrated in the device  10 . In a possible version the plates  11 , 11 ′ are mounted vertically and elastically to the outer case  13 , with switch or sensor  12  mounted to the inner side of plate  11 . Upon placing the measuring probe  14  the plates are pushed inside and via switch respectively sensor a signal is caused that will be transmitted to the control unit (e.g. micro processor). There the zero adjustment or calibration will be started. Alternatively, a solution is possible where the signal given by the sensors (e.g. an electromagnetic field or acoustic signal) will be detected by sensor  12  which is connected to reference plate  11  so that the plates can be fixed. 
     FIG. 2 shows a preferred version. The coating thickness measuring device  10  is equipped with a fixture for one or more measuring probes. Reference plates  11 ,  11 ′ are integrated in the fixture. In particular, it is advantageous to arrange two sensors  15 ,  15 ′ at opposite ends of a separate case  14  that should be smaller-than the case of the device  10 . Thus the fixture can be designed in a way that the case with the sensors can directly be put and locked in, the case of the device. Mounting of the measuring probes is facilitated by the ramps  16 . Both sensors  15 , 15 ′ of the measuring probe are pressed against the corresponding reference plates  11 , 11 ′. When taking out the measuring probe  14  it is activated and subsequently the zero adjustment or calibration of both sensors-starts via a switch or a special sensor while the sensors  15 , 15 ′ are still lying on the reference plate  11 , 11 ′. Activation can be made as follows: by unlocking the measuring probe  14  the reference plates  11 , 11 ′ are moved towards sensors  15 , 15 ′, thus the sensors are pushed into the case  14  and a switch is released in the case of the probe  14 . An alternative could be,that upon pushing the case of the probe  14  into the coating thickness measuring device  10  a pin  18  at the fixture that fits to a corresponding hole in the probe case releases a switch  17  of the probe. It is also possible to release and close an electrical contact directly between fixture and probe case  14 . 
     Of course, such a coating thickness measuring device is also possible for a measuring probe with only one sensor. In this case only one reference plate  11  is necessary in the fixture of the coating thickness measuring device  10 . Two reference plates  11 , 11 ′ arranged as shown in FIG. 2 are necessary if the probe is equipped with a sensor comprising two measuring principles. However if the measuring probe  14  only has one sensor  15 , the probe  14  is placed in the fixture such that the sensor  15  is directed towards the reference plate  11  or  11 ′ which corresponds to the measuring principle to be used after taking out the measuring probe. In this case, upon releasing the measuring probe a trial measurement will be taken to check which reference plate  11  or  11 ′ is concerned. Subsequently, the zero adjustment or calibration is started depending on the measuring principle assigned to the reference plate. Upon removing the gauge measurements are taken using this principle. If the measuring principle is to be changed, as for example measurements on a different substrate are to be taken, the sensor has to be inserted into the fixture with the sensor lying on the reference plate that is assigned to the measuring principle applicable to the other substrate. Upon a new release corresponding processes for the other measuring principle are started. Other solutions for a measuring probe with only one sensor as shown in FIG. 2 are possible. For example, the reference plate could be built horizontally into the fixture, so that the measuring probe is inserted with the sensor in front. In case of a measuring probe for two measuring principles the multiple sensor would be arranged in a position laterally displaced from the center axis of the case of the measuring probe  14 . Correspondingly the reference plates would be arranged at the left and right side of the axis of the case  10 . In order to select a certain measuring principle the measuring probe is inserted into the fixture with the sensor over the corresponding reference plate. 
     For a combined device to measure ferrous and non-ferrous metals only one reference plate is imaginable. In this case the steel sheet has a thin layer of a non-ferrous metal with a thickness of 20-50 μm. This thin non-ferrous layer is sufficient as for the measurement on non-ferrous metals high frequent electromagnetic fields (normally&gt;10 MHz) are used, Due to their “skin effect” they only have a penetrating depth of about 20 μm. In case of zeroing or calibration of the sensor for a measurement of steel the known thickness of the non-ferrous layer is considered. 
     The coating thickness measuring device in accordance with the previous description also allows the use of special-shaped measuring probes, where an adapter to release the zeroing or calibration is connected with the measuring probe. Instead of the probe this adapter which is equipped with above mentioned release mechanism is inserted into the fixture. Advantageously, the adapter has the same geometry as a single or multiple probe that can directly be inserted into the fixture. For example, a measuring probe can be realized whose sensor is mounted to a rod (possibly liftable like a telescope). This rod in turn is connected with the adapter either rigidly or by means of a cable. Upon releasing the adapter the measuring probe is automatically zeroed on an external reference plate. With this device coatings at spots difficult to reach or in tubes can be measured. Also other measuring probes can be realized so that with only one coating thickness measuring device different measuring probes can be used. 
     Integrated parts of the preferred version in accordance with FIG. 3 are the electronics to record probe signals  21  as well as a micro processor  23 . Thus immediately after receipt signals can be digitized, before they are transmitted to the coating thickness measuring device. This is advantageous in case of longer transmission distances as digitized data are less sensitive. Furthermore, temperature differences between measuring probe  14  and coating thickness measuring device  10  cannot cause errors, as the temperature correction of the measuring signal is already done in the measuring probe and digitized data, that are received by the coating thickness measuring device, only have to be converted into a coating thickness value by the device&#39;s micro processor  31 . 
     Measurements taken by one or more measuring probes  14  can be transmitted to the coating thickness measuring device  10  in different ways. The easiest way of transmission is via cable. In this case the power supply of the measuring probe can be made by cable as well. Alternatively, transmission can be made optically. In the preferred version data are transmitted wirelessly. In this case several transmission solutions are possible. In the easiest form measuring probe  14  is only equipped with a transmitter  24  that after taking measurements transmits the results to the coating thickness measuring device. The gauge itself is equipped with a receiver  35  as shown in FIG.  4 . Advantageously, the measuring value is sent three times in a row for data security and in order to detect and eliminate incorrect transmission. 
     Moreover, there is the possibility to have the correct data transmission indicated by the coating thickness measuring device via optical or acoustic signal. A further possibility could be a bi-directional transmission line. For this measuring probe  14  and coating thickness measuring device  10  need to have a transmitter  24 , 34  as well as a receiver  25 , 35 . Thus there is the possibility to send a return message to the measuring probe  14  by the microprocessor  31  of the coating thickness measuring device  10 , and the probe recognises whether the measuring result has been received correctly. If not, the microprocessor  21  of the measuring probe repeats the measuring procedure. Even in this case an optical or acoustic signal can indicate a correct or incorrect data transmission. Via a bi-directional transmission line probe-specific data (for example serial number, probe parameter), e.g. determined during calibration of the probe, can be transmitted to the probe. In this case, switch  17  and spike  18  as shown in FIG. 2 can be left out because individual commands (e.g. for zero adjustment) can be transmitted to the probe by the coating thickness measuring device. 
     An identification is transmitted together with the essential signal by means of which the coating thickness measuring device recognises which sensor or measuring principle was used. Thus the measuring result can be clearly identified, indicated and/or transmitted to another instrument (printer, computer). 
     In case of wireless data-transfer, the measuring probe is powered by a battery  26 . In a preferred version the measuring probe is equipped with an accumulator  26 . While the measuring probe is in the fixture of the coating thickness measuring device  10 , the accumulator  26  is being loaded by the charging electronics  32  of the device  10 . This is achieved by electric contacts between the measuring probe and the device or inductively. It is advantageous to have the charge condition of the battery respectively the accumulator  26  controlled by a battery charge control system which is regularly checked by the micro-processor  23 . If the charge condition of the battery/accumulator  26  falls below a defined level a signal is sent together with the data transmission. Advantageously, this signal appears in display  37  of the coating thickness measuring device  10 . 
     In addition to a display in the case the coating thickness measuring device  10  can be equipped with an interface  38  to connect the device, e.g. with a computer or printer. Via this interface  38  measuring data can be downloaded to a computer or printer for memorising and/or processing. Data and commands can also be uploaded into the device  10 . Advantageously, this interface is an infrared interface. Furthermore, the coating thickness measuring device  10  can be equipped with a memory  39  to store the measuring values taken by the probe  14  and transmitted to the device  10 . 
     For easier handling the back of the gauge can be equipped with a handle  19  that can be fixed in several positions. If folded up the handle clicks behind the device&#39;s guide rail  20  for serving as a fixing clip e.g. to attach the coating thickness measuring device to clothes. The handle can be easily folded by pressing the sides. The folding angle can be varied in order to place the device in a suitable leaning angle. This allows an easy one-handed use of the device and the user can concentrate himself on using the measuring probe  14 .