General Idea - RTD Module

Analog Value - A,

The value varied continuously such as voltage, current, temperature, speed, pressure, flow and so on are called analog values. For the example of temperature, it is continuously varied with time like Picture 1.1. Varied temperatures like this are processed as digital values by the RTD module in a PLC.

Digital Value - D,
The value shown as number such as 0, 1, 2 and 3, and varied non-continuously are called digital values. ON signal and OFF signal are shown as the digital value of 0 and 1. BCD values and binary values are also digital values.

To operate with digital values, analog values cannot be inputted directly to a CPU module.
Therefore, analog values is to be converted to digital values like Picture 1.4, being inputted to a CPU.
To output analog values, it is necessary to convert the digital values in a CPU to analog values.

Platinum Resistance Temperature Detector,

This is a sensor used to detect temperatures in the type of a resistance.
RTD Pt100 and RTD jPt100 indicate the output of 100.00 Ω for 0oC.
RTD Pt1000 indicates the output of 1000.00 Ω for 0oC.

Characteristics of Temperature Conversion,

The resistance values of a Pt100 are varied according to the variation of the temperature around it.
RTD modules linearize the non-linear resistance input of RTD as the above diagram.
Temperature values are stored in the memory of a RTD module in the converted temperature values.
A PLC CPU reads the converted temperature values stored in the memory of the RTD module.

Enabling/Disabling to RDT-Convert

It is available to assign enabling/disabling to RTD-convert to input channels.
As unused channels can be assigned to disabling to RDT-convert, the time for sampling is reduced

Detected Temperature Values

The centigrade or the Fahrenheit values of converted temperatures are stored in a memory.(Actual Temperature * 10)
Converted temperatures are converted to the values in the range from 0 to 16000.

Information about Operating Channels

The information on the currently operating channels is indicated.
In case of the breaking of the wires among the currently enabled channels, the corresponding bit is 0.
The bit corresponding to disabled channels is 0.

Detecting the Breaking of Wires

The breaking of the wires connected to a RTD for each channel can be checked.
If the breaking of wires is detected, a RTD module will keep the temperature value before broken and not convert anymore. Error code is indicated and LED blinks at the intervals of 0.3 sec.
In case that a shield line is connected or disconnected due to bad contact, a RTD module converts when connected and keeps current temperature value when disconnected. Error code is indicated and LED blinks at the intervals of 0.3 sec.

Setting up Digital Output

The range of the digital output values stored in a buffer memory can be selected as -192~16191 or -8192~8191.

Setting up Maximum and Minimum Temperature

RTD modules convert the temperatures from –200 to 600℃ to the digital values from 0(-8000) to 16000(8000). The maximum value and the minimum value of temperatures can be set up.
If a maximum and a minimum value are set up, RDT modules convert the minimum to 0(-8000) and the maximum to 16000(8000).