ANALOG to PULSE Temperature Transmitter.
The TC-003 uses a 24V DC signal pulse that is compatible with standard PLC digital inputs. This signal is extremely tolerant of external interference.
The temperature information is converted into a digital number format in the TC-003 so that electrical noise does not alter the temperature indication.
All of the high precision measurement and conversions are performed by the TC003.
Conventional systems using analog 4-20mA RTD transmitters have a number of sources of potential errors. Temperature drift and errors in the transmitter, electrical interference in the analog signal, and measuring errors and drift in the PLC or computer analog inputs
Careful inspection of the specifications of PLC analog input cards will show that some types have a specified error of up to 0.5% at high ambient temperatures.
The TC-003 has been developed to use the industry standard PT100 RTD sensor for process temperature. The PT100 sensor is constructed from purified platinum, and its temperature measuring relies on the electrical properties of the platinum. Platinum is a
stable and non-corroding metal so that its properties will remain constant over time.
The electrical behavior in relation to temperature is well known, and is published by International Standards authorities as the basis for the determination of temperature for highly accurate scientific work. The resistance change with temperature is not exactly
linear, but it follows a mild parabolic curve for which scientific research has given a practically exact formula. The microprocessor in the TC-003 is programmed with this formula, so that it can give a precise temperature measurement over a wide temperature
range of -100°C to +850°C.
It is interesting to note that many analog RTD (4-20mA) transmitters do not compensate for this curve and so their calibration process requires a compromise to minimize the
error, but it cannot eliminate it. Practically this means that the curve is ignored and the resulting errors are accepted, especially if the users are unaware of this behavior.