1 Introduction

The LX3V-4TC expansion module amplifies the signal from four thermocouple sensors (Type K or J) and converts the data into 12 bit reading’s stored in the main unit. Both Centigrade (°C) and Fahrenheit (°F) can be read.

Reading resolution is 0.2°C/0.72°F of Type K and 0.3°C/0.54°F of Type J.

All data transfers and parameter settings are adjusted via software control of the LX3V-4TC; by use of the TO/FROM applied instructions in the PLC.

LX3V-4TC consumes 5V voltage from LX3V main unit or active extension unit, 90mA current of power supply. Thermocouples with the following specifications can be used: Type K, Type J.

2 External dimensions

1. Extension cable and connector
2. Com LED: Light when communicating
3. Power LED: Light when connect to 24V
4. State LED: Light when normal condition
5. Module name
6. Analog signal output terminal
7. Extension module interface
8. DIN rail mounting slot
9. DIN rail hook
10. Mounting holes (φ4.5)

Using crimp terminations

3 Terminal Layouts

Unused channels should have a wire link connected between the + and – terminals to prevent an errors being detected on that channel.

• If there is excessive electrical noise, connect the FG terminal to the ground terminal on the unit.
• Connect the ground terminals of the LX3V-4TC module and the PLC. Use grounding on the PLC.
• The 24V DC built-in supply of the PLC may be used as the power supply.

4 Installation notes and usage

Environmental specification

Power supply specification

Performance specification

Analog input

Feature Conversion

Miscellaneous

Buffer memory

1. The LX3V-4TC module communicates with the PLC via buffer memories.
2. BFMs #21 to #27 and #31 are reserved. All non-reserved BFMs can be read by the PLC using the FROM instruction.
3. BFMs (buffer memories) marked with an “*” can be written to, the special function block using the TO instruction.

Buffer Memory BFM #0: Thermocouple Type K or J selection mode

BFM #0 is used to select Type K or J thermocouples for each channel. Each digit of a 4 digit hexadecimal number corresponds to one channel, the least significant digit being channel 1.

Example

• 0= Type K
• 1= Type J
• 3= Not used

• A/D conversion time is 240ms per channel. When “3" (unused) is set for a channel, A/D conversion is not executed for that channel, therefore, the total conversion time is decreased. In the above example, the conversion time is as follows:

240ms (conversion time per channel) × 2channels (number of channels used) = 480ms (total conversion time)

Buffer Memory BFMs #1 to #4: Number of temperature readings to be averaged

When the number of temperature readings to be averaged is specified for BFMs #1 to #4, the averaged data is stored in BFMs #5 to #8 (°C) and #13 to #16 (°F). Only the range 1 to 256 is valid for the number of temperature readings to be averaged. If a value outside of this range is entered, a default value of 8 is used.

Buffer Memory BFMs #9 to #12 and #17 to #20: Present temperature

These BFMs store the present value of the input data. This value is stored in units of 0.1°C or 0.1°F, but the resolution is only 0.4°C or 0.72°F for Type K and 0.3°C or 0.54°F for Type J.

States information

Buffer memory BFM#28: Digital range error latch

BFM #29 b10 (digital range error) is used to judge whether the measured temperature is within the unit’s range or not.

BFM #28 latches the error status of each channel and can be used to check for thermocouple disconnection.

• Low: Latches ON when temperature measurement data goes below the lowest temperature measurement limit.
• High: Turns ON when temperature measurement data goes above the highest temperature measurement limit, or when a thermocouple is disconnected.

When an error occur the temperature data before the error is latched. If the measured value returns to within valid limits the temperature data returns to normal operation. (Note: The error remains latched in (BFM #28))

An error can be cleared by writing K0 to BFM #28 using the TO instruction or turning off the power.

Buffer memory BFM#29: Error states

Identification Code Buffer Memory BFM #30

The identification code or ID number for module is read from buffer memory BFM #30 using the FROM command.

This number for the LX3V-4TC unit is K2030.

The PLC can use this facility in its program to identify the expansion module before commencing data transfer from and to the expansion module.

System block diagram

5 Example

In the program shown below, the LX3V-4TC occupies the position of special block number 2 (that is the third closest block to the PLC). A Type K thermocouple is used on CH1 and a Type J on CH2. CH3 and CH4 are not used. The averaging count is four. The averaged values in degrees C of input channels CH1 and CH2 stored respectively in data registers D0 and D3.

Example 1

This initial step checks that the special function block placed at position 2 is actually an LX3V-4TC, i.e. its unit identification number is 2030 (BFM #30). This step is optional, but it provides a software check that the system has been configured correctly.

• Specify the type of thermocouple, H3310 -> Block No.2 BFM#0. CH3 & CH4 are not used; CH2: Type J (1); CH1: Type K (0);
• Block No.2 BFM#30->(D2) identification code;
• When (K2030)= (D2), M1=ON. i.e. when identification code is K2030, M1=ON.

Example 2

Transfer the error status to (M25 to M10), when error is found, M10=ON

This step provides optional monitoring of the LX3V-4TC Error Buffer Memory (#29). If there is an Error on the LX3V-4TC, bit b0 of BFM #29 will be set on. This can be read by this program step, and output as a bit device in the PLC (Y010 in this example). Additional Error devices can be output in a similar manner, e.g. b10 BFM #29 Digital range error. (see example 3)

Example 3

M10 represents b0 of BFM#29

M20 represents b10 of BFM#29

• (K4)-> (BFM#1), (K4)-> (BFM#2). Number of samples is changed to 4 on both CH1 and CH2.
• (BFM#5)-> (D0), (BFM#6)-> (D1). Transfer the average temperature value in °C to the data registers.

This step is the actual reading of the LX3V-4TC input channels. It is essentially the only program step which is needed. The "TO" instruction in this example, sets the input channels, CH1 and CH2, to take the average reading of four samples.

The "FROM" instruction reads the average temperatures (BFM #5 to #8) for input channels CH1 and CH2 of the LX3V-4TC. If direct temperature readings are required BFM #9 and #10 should be read instead, e.g.

6 Diagnostics

Preliminary checks

1. Check whether the input wiring and/or extension cables are properly connected on LX3V-4TC analog special function block.
2. Check that the LX3V system configuration rules have not been broken, i.e. the number of special function blocks does not exceed 16 and the total system I/O is equal or less than 256 I/O.
3. Ensure that the correct operating range has been selected for the application.
4. Check that there is no power overload on either the 5V or 24V power sources, remember the loading on a LX3V main unit or a powered extension unit varies according to the number of extension blocks or special function blocks connected.
5. Put the LX3V main unit into RUN.

Error checking

If the LX3V-4TC special function block does not seem to operate normally, check the following items.

Check the status of the POWER LED.

Lit: The extension cable is properly connected.

Otherwise: Check the connection of the extension cable.

• Check the external wiring.
• Check the status of the “24V” LED (top right corner of the LX3V-4TC).

Lit: LX3V-4TC is OK; 24V DC power source is OK.

Otherwise: Possible 24VDC power failure, if OK possible LX3V-4TC failure.

• Check the status of the “A/D” LED (top right corner of the LX3V-4TC).

Lit: A/D conversion is proceeding normally.

Otherwise: Check buffer memory #29 (error status). If any bits (b2 and b3) are ON, then this is why the A/D LED is OFF.

Checking special function block numbers

Other special units of blocks that use FROM/TO commands, such as analog input blocks, analog output blocks and high-speed counter blocks, can be directly connected to the base unit of the LX3V programmable controller or to the right side of other extension blocks or units. Each special block is consecutively numbered from 0 to 15 beginning from the one closest to the base unit. A maximum of 16 special blocks can be connected.

7 EMC considerations

• Electromagnetic compatibility or EMC must be considered before using the LX3V-4TC.
• WECON recommends that the thermocouple sensors used, should be fitted with a form of seild or screening as protection against EMC noise.
• If some form of cable protection is used, the “Shield” must be terminated at the terminals as shown in chapter 3.
• Because of the delicate nature of all analog signals, failure to take good EMC precautions could lead to EMC noise induced errors; up to ±10% of actual values. This is an absolute worst case figure, users who do take good precautions can expect operation within normal tolerances. EMC considerations should include selection of good quality cables, good routing of those cables away from potential noise sources.
• Additionally it is recommended that signal averaging is used as this will reduce the effects of random noise “spikes”