P generally represents the instrument, T generally represents the transformer.
According to GB 7159 "electrical technology in the development of symbols in the general rules" of electrical engineering and electrical equipment commonly used basic symbols: P, measuring equipment, test equipment. Can indicate that the device, recording device, cumulative measurement device, signal generator.
For example: PA stands for ammeter, PC stands for (pulse) counter, PJ stands for power meter, PS stands for recording device, PT stands for clock, operation schedule, PV stands for voltmeter.
Extended information:
Other meanings of P and T: There is a block of P and T settings on the telephone; p is pulse dialing and t is tone dialing. This is the selection mode for pulling numbers, pulse is where pressing 1 sends out a pulse signal, and so on. Dual-tone multi-frequency is to have two audio frequencies superimposed into a dual-tone signal,twelve buttons are distinguished by seven audio frequencies.
In the electrical diagram, P and T in the first letter stands for pressure and temperature, in the second letter is not. T first letter is the temperature, the second on behalf of the transmission, change to the meaning.
For example: PT is the pressure transmitter, PG is the pressure field display meter, TT is the temperature transmitter, TG is the field display thermometer
The two a ball valve, a gate valve.
T on behalf of the transformer, TA on behalf of the current transformer, TC on behalf of the control circuit power supply transformer, TI on behalf of the inverter transformer, TM on behalf of the power transformer, TP on behalf of the pulse transformer, TV on behalf of the voltage transformer.