E and T denote the sensing element and transmitter respectively; so when to use TT (PT) and when to use TE (PE)?
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On the attachment (PID diagram), one is marked with E (TE) and the other with T (PIT).
E is the sensing element; there is no sensing element for pressure! Just take the pressure directly! Temperature is generally measured using sensors such as thermocouples and thermal resistors. When regulation or interlocking is required, on-site conversion is usually needed, for which TT is utilized. Flow rates generally have FE and FT; common examples include throttle devices (FE) and differential pressure transmitters (FT).
Please make sure you understand what these letters in the PID diagram represent first
T: Transmitter, which refers to the process of converting the variable being measured into a standard signal, such as 4~20mA； E: Element, referring to components or sensors that convert the variable to be measured into signals, such as millivolts, resistance, pulses, frequency, etc. Tables used for visual observation that are not converted into signals, such as pointers and liquid columns, cannot be represented by T or E. A pressure gauge can use PG, but not PE.
Use TT (PT) or TE (PE)? 1. It depends on the signal requirements; for example, if the subsequent receiving device requires a standard signal (4~20mA), then TT (PT) should be used, while if the receiving device can accept non-standard signals, then TE (PE) can be used； 2. Generally speaking, 4–20mA signals have better noise resistance compared to millivolt signals ； The environmental impact is also smaller ； 3. Installation requirements: generally, factors such as the ambient temperature at the installation location, electromagnetic interference, and transmission distance. . . . . .
Are they TE or PE instruments, allowing parameter viewing on-site? If parameters need to be viewed in the control room, then TT and PT must be converted into current signals for transmission
To determine whether the parameters can be viewed on-site for TE and PE instruments, it is necessary to check whether these instruments have on-site display gauges that show the values as they convert the variables being measured into signals. If not, the parameters cannot be viewed on-site. Because humans cannot see millivolts, resistance, pulses, or frequency.
Then PE and TE must include PT and TT as well; otherwise the data detected by the sensor is useless
No, for example, with thermal resistors, they are connected directly to the thermal resistor input card without going through a transmitter, or to instruments that can directly receive the resistance signal； For example, with thermocouples, they can be connected directly to the thermocouple input card without a transmitter, or to instruments that can directly receive the signal from the thermocouple ； There is also a pulse input card that can directly receive pulse inputs.
The four main parameters of instruments are pressure P, flow rate F, liquid level L, and temperature T; whenever the initial letter is one of these, it refers to that parameter. E is the measuring element. TE refers to the temperature measurement element, namely thermal resistors and thermocouples on-site. TIA I indicates that A represents an alarm; it is a temperature display alarm function, and this is what is shown on the computer (displayed on the DCS). The meanings of various character symbols are shown in the table