Adjustment (technology)
In electronics, adjustment (also trimming ) is a setting
- in the sense of a zero adjustment as part of a measurement that works on the principle of compensation , e.g. B. when using a Wheatstone bridge or a voltage compensator ; a comparison variable is set to the measured variable up to the difference display zero ,
- in the sense of an adjustment for the production and maintenance of the operability of components, technical devices and systems; one or more parameters are set for proper operation.
The adjustment is a setting ; it is to be distinguished from the calibration , which is a measurement and is carried out without interfering with the measuring device ( DIN 1319-1). When establishing the extent to which a measuring device complies with certain regulations associated with calibration , one speaks of calibration in the case of legal competence .
Operations during proper operation and for switching on, starting, etc. are part of the operation and are carried out via a user interface .
requirements
The prerequisites for the adjustment are the supply of a suitable test signal, the establishment of an operating state specified in the adjustment specification and the connection of the suitable measuring equipment . The calibration rule also defines the calibration criterion (compare the target value and tolerance range with the measurement) and the actuating element.
For example, when setting the zero point of moving-coil measuring mechanisms, the prescribed, steady position of the device and unconnected (free) connections are required. With such measuring devices, a symbol on the scale or another visible surface indicates the installation or operating position. Statements on guaranteed error limits only apply if specified reference conditions are observed .
When manufacturing components in electronics or also when balancing, the processes are (partially) automated and usually do not use an actuating element, but change the parameters through material removal or application, through heating or purely electronically, for example by writing to an EEPROM , which digitally records the adjustment values saves. The calibration specification is stored as software in the production system, the remaining measurement deviation is often determined by comparison with a reference variable / a reference component.
Need for recruitment
The need for adjustment / trimming arises from the inaccuracy or instability of technical parameters:
- temporal drift due to aging or external influences (see also bias (electronics) )
- changing conditions of use (moving to different ambient conditions / heat / humidity) or e.g. B. changed loading (watercraft and aircraft, see also trim )
- principally imprecise manufacturing technologies
- of components: these are often trimmed or adjusted to the target value at the end of the manufacturing process (examples: resistance adjustment, offset voltage adjustment for operational amplifiers , balancing of rotating parts)
- of devices: here set parameters are often set manually by adjustment or trimming during commissioning. Adjusting screws, control valves, trimming capacitors or trimming potentiometers are used for this purpose , but the process can also be carried out electronically, automatically or using internal software.
Too frequent adjustments can impair the stability due to wear of the operating elements and lead to increased maintenance .
The (re) establishment of the tuning of musical instruments is called tuning . In the case of radio receivers, the setting of the reception frequency (operating procedure) is also referred to as tuning , while the setting of the oscillator or filter frequencies during commissioning is referred to as adjustment .
Setting guideline
Another name for the adjustment rule is setting guidelines or setting instructions . The difference in content lies in the degree of commitment and the frequency of execution. The adjustment takes place after the production of a device in the test field or after a repair (e.g. by a measuring or calibration service). The setting is often also made by the operator (fitter, operations service).
Adjusted or calibrated devices or components are often glued, sealed with lacquer or even lead- sealed in order to rule out unauthorized adjustments, environmental influences or changes in position.
Calibration services provide a measurement report from which the calibration result and compliance with the tolerances can be seen.
In order to maintain the tolerances specified for the television signal or color television signal, the technical systems (studio, outside broadcast vehicle, radio relay systems, etc.) were set according to a setting specification. This regulation was necessary because setting procedures with several actuating elements do not necessarily lead to the required operating parameters in the event of a deviation from a specified sequence. In the GDR, this setting was the task of the operations department of the studio technology television , the setting guidelines were drawn up by the Central Radio and Television Office .
Adjustment technology
A distinction must be made between one-dimensional and multi-dimensional balancing or setting processes. A one-dimensional setting is e.g. B. setting the zero point of a scale.
With two-dimensional adjustment processes, compliance with two criteria must be achieved with the aid of two actuating elements. Although this task can also be solved by laypeople (e.g. contrast and brightness for television, tuning and feedback for the single-circle, symmetry and active spring length for the balance wheel ), a technology should generally be specified. If the technology is wrong, divergence occurs and the more or less simultaneous fulfillment of both criteria is not achieved.
- Example TV picture: The TV set has controls for the operating point and the gain , which are referred to as brightness and contrast. The two criteria are the brightness for the white level and that for the black level (cut-off point of the picture tube). Depending on the design, the setting criterion for the brightness can be at one of these two values (or very unfavorably at an intermediate value). The setting criterion for the contrast is then the other value, preferably the white value.
Two-dimensional matching processes often require an iteration that does not lead to success if the sequence is not followed. Examples:
- adjusting two mirrors to align a laser beam along an optical axis
- Adjustment of inductances and capacitances in a superimposition receiver in order to achieve synchronization of the oscillator and pre-circuit
- Example of convergence: An example of a multi-dimensional adjustment is the convergence setting in CRT color television sets or color picture tubes . Such multi-dimensional adjustment processes are rather hopeless without aids. Therefore, the second generation of color television receivers had what is called a matrixed convergence setting. The decoupling of the criteria through circuitry measures (matrixing) can be replaced by measuring the deviations and converting them to the necessary adjustment of the actuating elements using software.
Setting guidelines are almost always structured in such a way that a setting that is intrinsically multidimensional is broken down into a maximum of two-dimensional processes (e.g. operating point and gain) with a specified sequence. Iterations cannot always be avoided.
- Example of ignition setting: In the past, gasoline engines had mechanical interrupters for ignition. The contact spacing of the interrupter contacts and the ignition times had to be set . The setting technology in the Wartburg two-stroke engine consists of one-dimensional setting processes.
- The contact distances are set with a gauge held between the contacts. The crankshaft must be turned to the position with the greatest contact distance. The ignition times of all three cylinders are adjusted at the same time by turning the breaker plate, as it carries all three breaker contacts. Only one of the contacts can be checked. The other two contacts are readjusted (corrected) after the setting of the first contact has been completed. The setting criterion is the interruption of the circuit (ignition) a few millimeters before the top dead center of the first cylinder (check with a stroboscope + marking lines or with a dial gauge instead of the respective spark plug).
Modern gasoline engines have Hall sensors for controlling the ignition timing and do not require any adjustment. In addition, control units can vary the ignition timing not only as a function of engine speed, but also as a function of load, temperature and fuel. For this purpose, an engine map is stored in them. This so-called map control can be digitally compared to different wishes or requirements (e.g. "sporty" or economical).
Trends
The calibration and setting technology is a mandatory part of the device development and should be as simple as possible or avoided from the outset. Modern, automated, more precise manufacturing methods can avoid or automate matching processes. With digital technology ( digital signal processing ), which is becoming more and more widespread, calibration is no longer required for the function of the digital part itself. There, however, data series can be stored that are obtained individually during commissioning and describe and correct linearity deviations or manufacturing inaccuracies of analog components of a device. Due to the cost-effective data processing of many sensor signals, manual comparison can often be dispensed with, which reduces manufacturing and maintenance costs.
Individual evidence
- ^ VEB Automobilwerk Eisenach (ed.): Operating instructions for the passenger car WARTBURG 353 W Limousine Tourist . VEB Fachbuchverlag Leipzig, Leipzig 1982, p. 55 .