Tronic Pressure Transmitters and Transducers
All WIKA Tronic pressure transmitters and transducers convert an applied pressure into an electrical signal. This signal is sent to computers, PLC's (programmable logic controllers), chart recorders, digital panel meters or other devices that interpret this electrical signal and use it to display, record, and/or change the pressure in the system being monitored. The most popular signal used in industrial applications is a 4-20 milliamp (mA) 2 wire current loop. Other signals used include 1-5 volts, 0-5 volts, 0-10 volts (3 wire systems) and 0-100 millivolts (4 wire systems). In many cases the display device that the transmitter is connected to can accept more than one type of output - for example, 4-20 mA or 0-5 volts. Because of its popularity, WIKA stocks a large inventory of 4-20 mA output transmitters in many different models. By convention a pressure transmitter provides a mA output while a pressure transducer provides a voltage output. Many users refer to transmitters and transducers interchangeably. This can create some confusion, but it may be helpful to note that general purpose pressure sensors are most commonly referred to as pressure transducers. Linearity What makes these devices useful is that the output, regardless of type, is linear. This means that the output is directly proportional to the applied pressure. WIKA transmitters are fixed range devices, and are described in part by pressure range and output type. For example, a transmitter with a 0-100 psi range and 4-20 mA output would produce a 4 mA output at 0 pressure and 20 mA at 100 psi.
Because the transmitter output is linear, it will directly relate to the applied pressure. At 25 psi, the output will be 8 mA; at 50 psi, 12 mA; and at 75 psi, 16 mA. If the device reading this mA signal is a programmable panel meter, it can convert the 4-20 mA signal to 0-100 psi and display the pressure on the digital readout. Since the 4-20 mA is consistent, the meter can be programmed to display any engineering units desired. If a BAR reading is required, the meter is programmed to display 0 bar at 4 mA and 6.89 bar at 20 mA. The meter circuitry completes all other calculations automatically. Accuracy The straight line shown above represents an ideal, perfectly linear output. In reality, errors are introduced into the output signal by the various transmitter components. The amount of error introduced refers to the deviation from the ideal straight line.
"Accuracy" most commonly refers to the percent deviation from the ideal. It can also be calculated using linearity, hysteresis, and repeatability values. Most WIKA transmitters have less than a 0.25% linearity deviation over the span. See the specifications section for each model number for detailed information. In industrial applications, repeatability is usually more important than "full scale accuracy" matching a traceable standard. WIKA transmitters feature excellent repeatability - less than 0.05% span for most models. When comparing accuracy, note there are many different ways manufacturer calculate accuracy. Be sure to consider temperature compensation, as industrial environments rarely match the laboratory conditions sometimes used by other transmitter manufacturers when determining accuracy. Performance WIKA transmitters and transducers are designed for long term, reliable performance in difficult industrial environments. Most models feature stainless steel construction, moisture, and vibration protected circuitry, and all are calibrated and tested prior to shipment. A variety of options are available on most models to meet specific needs. Applications WIKA transmitters are available in many different models that have features to meet the needs of specific applications. Model types are described below.
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