The measurement of electric current strength is not always easy, especially when the measured signal requires further electronic conditioning. Simply connecting an ammeter to an electrical circuit and reading out the value is no longer enough. The current signal must be fed into a computer in which sensors convert current into a proportional voltage with minimal influence on the measured circuit.
The basic sensor requirements are galvanic isolation and a high bandwidth, usually from DC up to at least 100 kHz. Conventional current measurement systems therefore tend to be physically large and technically complex.
Conventional sensors are physically large and technically complex; also they have disadvantages as stated above. Hence they are replaced by magnetoresistive current sensors. The magnetic field sensors are based on the magnetoresistive effect. These sensors can be easily fabricated by means of thin film technologies wit widths and lengths in the micrometer range. To reduce temperature dependence, they are usually configured as a half bridge or a full bridge. In one arm of the bridge, the barber poles are placed in opposite directions above the two magnetoresistors, so that in the presence of a magnetic field the value of the first resistor increases and the value of the second decreases.
It is found that changing the orientation of the magnetic moment in the wire caused a current passing through it to change correspondingly. The orientation could be changed by apply in an external magnetic field, and generally an increase in current was observed. This phenomenon is called anisotropic magnetoresistive effect.
The ferromagnetic materials can be deposited as thin films and structured into small strips that are typically 40mm thick,10mm wide, and 100mm long. In most general case, the electrical resistance of AMR material depends on the angle between the direction of the magnetization, and the direction of the current going through it. When the current and magnetic moment are parallel, the resistance of the strip is greatest; when they are at a 90 degree angle to each bother, it is smallest.
Magnetoresistive field sensors are usually configures as a half or full bridge. The barber poles are positioned such that in the presence of magnetic field the value of first resistor increases and that of second decreases.
The ferromagnetic materials can be formed into thin films and can be structured into small strips that are typically 40mm thick, 10mm wide and 100mm long. This makes the fabrication of the sensor very easy
Measured quantity is directly proportional to the output. The current flowing through Permalloy conductor generates a magnetic field that exactly compensates the magnetic field generated in the conductor that is to be measured. Hence the device is linear.
Magnetoresistive sensors are not affected by the external magnetic field. This is achieved by the full bridge configuration of four magneto resistors. Barber poles have the same orientation in the two arms, so no external field will affect the system.
Magnetic field sensors based on the magnetoresistive effect can be easily fabricated by means of thin film technologies with widths and lengths in micrometer range. For best performance, these sensors must have a very good linearity between the measured quantity and the output signal. Even when improved by the barber poles, the linearity magnetoresistive sensor is not very high, so the compensation principle used on hall sensors is also applied here. An electrically isolated aluminum compensation conductor is integrated in the same substrate above the Permalloy resistors.
The current flowing through this conductor generates a magnetic field exactly compensates that of the conductor to be unmeasured. In this way the MR element always work at the same operating point; their nonlinearity therefore becomes irrelevant. The temperature dependence is also almost completely eliminated. The current in the compensation conductor is strictly proportional to the measured amplitude of the field; the voltage drop across a resistor forms the electrical output signal.
Magnetoresistive sensors, as are hall elements are very well suited or the measurement of electric currents. In such applications it is important that external magnetic fields do not distort the measurement. This achieved by forming a full bridge are specially separated. The barber poles have the same orientation in the two arms, so that only a field difference between the two positions is sensed. This configuration is insensitive to external homogenous perturbation fields. The primary conductor is U shaped under the substrate, so that the magnetic fields acting on the two arms of the bridge have the same amplitude but opposite directions. This way the voltage signals of the two half-bridges are added.
The sensors require neither a core nor a magnetic shielding, and can therefore be assembled in a very compact and cheap way. The output is calibrated by a laser trimming process or by a digital calibration.
Digital radiography sensors are also considered semicritical and should be protected with a Food and Drug Administration (FDA)-cleared barrier to reduce contamination during use, followed by cleaning and heat-sterilization or high-level disinfection between patients. If the item cannot tolerate these procedures then, at a minimum, protect with an FDA-cleared barrier. In addition, clean and disinfect with an Environmental Protection Agency (EPA)-registered hospital disinfectant with intermediate-level (i.e., tuberculocidal claim) activity between patients. Because these items vary by manufacturer and their ability to be sterilized or high-level disinfected also vary, refer to manufacturer instructions for reprocessing.
A signal conditioners primary purpose is to convert the signal produced by any given sensor into a more usable form. A variety of sensors are used in industrial applications to measure and/or monitor several different parameters. Each sensor may have unique signal processing requirements, including excitation voltage, signal amplification, filtering, linearization, etc. S. Himmelstein and Company offers flexible signal conditioners that can be easily configured to satisfy the needs of these different sensors.
Once the signal is processed, it can then be re-transmitted in a more universal format, such as ±10 Vdc, 4-20 mA or digital, to other instrumentation. S. Himmelstein and Company signal conditioners will also provide local digital display of the processed signal, and additional functions such as cross channel calculations with math operations, limit checking with alarm notifications, max and min data capture, tare and hold functions, etc.
Many measurement sensor output characteristics can be low level dc current or voltage, or frequency signals. Conditioning the low level signals requires amplification, frequency signals are processed with a frequency to voltage converter. These signals can also be affected by electrical noise, such as from variable frequency drives, or mechanical noise caused by vibration. Using 7 pole antialiasing hardware filters, and 4 pole user settable digital filters with 10X oversampling, the signal conditioner will remove these noise components and allow only valid data to pass through.
For more than 30 years TE Connectivity's (TE) Measurement Specialties sensors have been designed to address the most demanding engineering challenges across a wide range of industries and applications. TE Connectivity Sensors measure pressure/force, position, vibration, temperature, humidity, and fluid properties and are at the heart of many everyday products and provide a vital link to the physical world.
The PASPORT Salinity Sensor works with the 10X Salinity Sensor Probe to measure the salinity, conductivity, and temperature of fresh to brackish water sources. The sensor determines salinity based on electrical conductivity. It also features a built-in calculation, based on the Practical Salinity Scale (PSS), that compensates for changes in conductivity caused by temperature changes.The Salinity Sensor measures the electric current through a solution between the two platinum electrodes in the Salinity Sensor Probe. The current through the solution is due to the movement of ions, so the higher the concentration of ions in the solution, the higher its conductivity. A voltage (AC) is applied across the two electrodes in the tip of the probe and the measured current is proportional to the conductivity of the solution.
Consider an all-in-one, touchscreen data collection, graphing, and analysis tool for students. Designed for use with wired and wireless sensors, the SPARK LXi2 Datalogger simultaneously accommodates up to five wireless sensors and includes two ports for blue PASPORT sensors. It features an interactive, icon-based user interface within a shock-absorbing case and arrives packaged with SPARKvue, MatchGraph!, and Spectrometry software for interactive data collection and analysis. It can additionally connect via Bluetooth to the following interfaces: AirLink, SPARKlink Air, and 550 Universal Interface.
HART provides two simultaneous communication channels, one analog, the other digital: A 4-20mA signal communicates the primary measured value (PV) as an analog value of current using the wiring that provides power to the instrument. The host system then converts the current value to a physical value according to parameters defined by HART Software. For example, 7 mA = 80 degrees F.
The HART Protocol communicates at 1200 bps without interrupting the 4-20mA signal and allows a host application (master) to get two or more digital updates per second from a smart field device. As the digital FSK signal is phase continuous, there is no interference with the 4-20mA signal. The HART Protocol provides two simultaneous communication channels: the 4-20mA analog signal and a digital signal. The 4-20mA signal communicates the primary measured value (in the case of a field instrument) using the 4-20mA current loop - the fastest and most reliable industry standard. Additional device information is communicated using a digital signal that is superimposed on the analog signal. 2b1af7f3a8