Control Technologies 2500 Series Operating instructions

Control Technology Inc.
5734 Middlebrook Pike
Knoxville, Tennessee 37921
www.controltechnology.com
Toll Free: 800-537-8398
2500 Series ™
Compact I/O System
2500C-8-TC
8-CHANNEL THERMOCOUPLE INPUT MODULE
2500 SERIES® COMPACT I/O
INSTALLATION AND OPERATION GUIDE
Version 1.2

Copyright© 2021 Control Technology Inc.
All rights reserved.
This manual is published by Control Technology Inc. (CTI) 5734 Middlebrook Pike,
Knoxville, TN 37921. This manual contains references to brand and product names which
are trade names, trademarks, and/or registered trademarks of Control Technology Inc.
Siemens®, SIMATIC®, and Series 505®, and 505®are registered trademarks of Siemens AG.
Other references to brand and product names are trade names, trademarks, and/or
registered trademarks of their respective holders.
DOCUMENT DISCLAIMER STATEMENT
Every effort has been made to ensure the accuracy of this document; however, errors do
occasionally occur. CTI provides this document on an “as is” basis and assumes no
responsibility for direct or consequential damages resulting from the use of this document.
This document is provided without express or implied warranty of any kind, including but not
limited to the warranties of merchantability or fitness for a particular purpose. This
document and the products it references are subject to change without notice. If you have a
comment or discover an error, please call us toll-free at 1-800-537-8398 or email us at
[e-mail].
REVISION HISTORY
Revision
Date
Description
1.0
4/15/2014
Initial Release
1.1
1/6/2020
Clarified reference from Offset Scaling to Scaling. Corrected
Figure 26 and 27 Reference.
1.2
1/11/2021
Corrected errors in Section 1.9. Scaling Enabled and Disabled
reference were incorrect. Default Shipping Configuration was
incorrect. Correct configuration was Scaling Enabled.
Removed Table in Section 1.6

2500C-8-TC Installation and Operation Guide
i
PREFACE
This Installation and Operation Guide provides reference information for the CTI 2500C-8-
TC 8-Channel Thermocouple Module for 2500 Series® Compact I/O system. We assume
you are familiar with the operation of CTI 2500 Series® programmable controllers. Refer to
the appropriate user documentation for specific information on the 2500 Series®
programmable controllers and I/O modules.
This Installation and Operation Guide is organized as follows:
Chapter 1 provides a description of the module.
Chapter 2 covers installation, setup, and wiring.

USAGE CONVENTIONS
NOTE
Notes alert the user to special features or procedures.
CAUTION
Cautions alert the user to procedures that could damage equipment.
WARNING
Warnings alert the user to procedures that could damage equipment and endanger the user.

2500C-8-TC Installation and Operation Guide
3
TABLE OF CONTENTS
USAGE CONVENTIONS.........................................................................................II
TABLE OF FIGURES ..............................................................................................5
CHAPTER 1................................................................................................... OVERVIEW..........6
1.1 Introduction.....................................................................................................6
1.2 Front Panel Description .................................................................................6
1.2.1 Status Display.................................................................................………..7
1.2.2 I/O Wiring Connector…………………………………………………………..7
1.3 Asynchronous Operation...............................................................................7
1.4 Modes of Operation........................................................................................7
1.4.1 Classic Mode..................................................................................………..8
1.4.2 Classic Plus Mode..........................................................................…….….8
1.5 Input Signal Ranges.......................................................................................9
1.6 Measurement Resolution...............................................................................9
1.7 Accuracy...................................................................................................... 10
1.8 Digital Word map......................................................................................... 10
1.9 Thermocouple Input to Digital Conversion................................................. 11
1.9.1 Scaling Enabled..............................................................................………11
1.9.2 Scaling Disabled.............................................................................………11
1.10 Effect of Out-of-Range Input Signals.......................................................... 12
1.11 Error Code Values Reported to the PLC.................................................... 15
1.12 Module Setup from the PLC in Classic Plus Mode.................................... 16
CHAPTER 2 INSTALLATION & SETUP..............................................................17
2.1 Installation Planning.................................................................................... 17
2.1.1 Safety Considerations....................................................................………17
2.1.2 Electrical Interference.....................................................................………18
2.1.3 Grounding.......................................................................................………18
2.2 2500C-8-TC Board Layout.......................................................................... 19
2.2.1 Defining Operation Mode and Range Selections ..........................………20
2.2.2 Power Requirements......................................................................………20
2.3 Unpacking the Module................................................................................ 20
2.4 Configuring the Module............................................................................... 20
2.4.1 Operation Mode Jumpers - Selecting Operation Mode.................………21
2.4.2 Selecting millivolt or Thermocouple Types for Each Channel......………22
2.4.3 Factory Default Settings.................................................................………22
2.5 Physical Installation..................................................................................... 23
2.6 Connecting Field Wiring.............................................................................. 24
2.6.1 Understanding the Modified Front Panel Connector………………………25
2.6.2 Connecting Thermocouple Input Wiring ........................................………25
2.6.3 Connecting the Shield Wiring.........................................................………26
2.7 Installing the Screw Terminal Connector ................................................... 26

2500C-8-TC Installation and Operation Guide
4
2.8 Calibration of the Module.............................................................................26
2.9 Checking Module Operation........................................................................27
CHAPTER 3 TROUBLESHOOTING.....................................................................28
APPENDIX A MODULE SPECIFICATIONS..........................................................29
CTI WARRANTY....................................................................................................31
REPAIR POLICY ...................................................................................................33

2500C-8-TC Installation and Operation Guide
5
Table of Figures
Figure 1 2500C-8-TC Front Panel.........................................................................................6
Figure 2 Asynchronous Operation Diagram...........................................................................7
Figure 3 2500C-8-TC Default Configuration Table ................................................................8
Figure 4 2500C-8-TC Classic Plus Login Table.....................................................................8
Figure 5 2500C-8-TC Classic Plus Configuration Options.....................................................9
Figure 6 2500C-8-TC Thermocouple Measurement Ranges.................................................9
Figure 7 2500C-8-TC Accuracy Rating Table......................................................................10
Figure 8 2500C-8-TC Digital Word Map Diagram................................................................10
Figure 9 2500C-8-TC Example of Change in Input Level ....................................................11
Figure 10 2500C-8-TC Example of Change in Input Level ..................................................12
Figure 11 2500C-8-TC Effect of Voltage Input on Type J Thermocouple.............................12
Figure 12 2500C-8-TC Effect of Voltage Input on Type J Thermocouple............................13
Figure 13 2500C-8-TC Effect of Voltage Input on Type T Thermocouple ...........................13
Figure 14 2500C-8-TC Effect of Voltage Input on Type E Thermocouple...........................13
Figure 15 2500C-8-TC Effect of Voltage Input on Type R Thermocouple...........................13
Figure 16 2500C-8-TC Effect of Voltage Input on Type S Thermocouple...........................14
Figure 17 2500C-8-TC Effect of Voltage Input on Type N Thermocouple...........................14
Figure 18 2500C-8-TC Effect of Voltage Input on mV Input................................................14
Figure 19 2500C-8-TC Error Code Table ...........................................................................15
Figure 20 2500C-8-TC Word Map for Configuration Data...................................................16
Figure 21 2500C-8-TC Binary Example of Module Configuration Word..............................16
Figure 22 2500C-8-TC Board Layout Picture......................................................................19
Figure 23 2500C-8-TC Operation Mode Jumpers Picture...................................................21
Figure 25 2500C-8-TC Jumper Signal Selection Table.......................................................22
Figure 25 2500C-8-TC Channel Thermocouple or Millivolt Selection Jumpers...................22
Figure 26 2500C-8-TC Range Selection Jumpers..............................................................22
Figure 27 2500C-8-TC Default Factory Settings.................................................................22
Figure 28 2500C-8-TC Module Physical Installation Picture...............................................23
Figure 29 2500C-8-TC Wiring Connector Diagram.............................................................24
Figure 31 Millivolt Wiring Connector Diagram....................................................................25
Figure 32 Thermocouple Wiring Connector Diagram.........................................................25
Figure 32 2500C-8-TC Thermocouple Type and Wire Descriptions....................................25
Figure 33 2500C-8-TC LED Error Code Table....................................................................27

2500C-8-TC Installation and Operation Guide
6
CHAPTER 1 OVERVIEW
1.1 Introduction
The CTI 2500C-8-TC Eight-Point Thermocouple Input Module is a member of Control
Technology’s family of I/O modules compatible with the Compact System Chassis. It is
designed to translate a J, K, T, E, R, S, N thermocouple or millivolt input signal from the field
device into an equivalent digital word which is then sent to the programmable controller
(PLC).
Features
•8 Thermocouple inputs
•Supports Classic and Classic Plus Modes
•7 Segment Display for Module Status indication
•No user calibration
•Supports J, K, T, E, R, S, & N thermocouples and millivolt inputs
•Software Configurable Range Selection
•Uses 2500C-32F-CJC removable wiring connector(sold separately)
1.2 Front Panel Description
The module front panel includes a 7-segment status display for showing module status, and
a 32-pin removable I/O wiring connector.
Figure 1 2500C-8-TC Front Panel
Status display
I/O wiring connector
with built in CJC

2500C-8-TC Installation and Operation Guide
7
1.2.1 Status Display
The Status Display will be illuminated with a “0” when the module is functioning normally. If
the Status Display is not lit or if it displaying something other than “0”, refer to Chapter 3 for
troubleshooting.
1.2.2 I/O Wiring Connector
The 2500C-8-TC utilizes a modified 32 pin connector, part number 2500C-32F-CJC (a
standard connector is NOT interchangeable) to provide wiring terminals for Channels 1-8
thermocouple inputs and two temperature (cold junction compensation) sensors. The wiring
connector accepts 14-22 AWG wire.
1.3 Asynchronous Operation
The module operates asynchronously with respect to the PLC (a scan of the PLC and input
sampling of the module do not occur at the same time). Instead, the module will translate all
analog inputs in one module update (3.5 milliseconds maximum) and store the translated
words in buffer memory. The PLC retrieves the stored words from the module buffer
memory at the start of the I/O scan.
Figure 2 Asynchronous Operation Diagram
1.4 Modes of Operation
The 2500C-8-TC supports two modes of operation: Classic mode and Classic Plus mode.
These two modes are selected by jumper JP11 located at the top of the card. Refer to
Figure 22 2500C-8-TC Board Layout Picture for the location of this jumper. Classic Mode is
the default shipping selection.

2500C-8-TC Installation and Operation Guide
8
1.4.1 Classic Mode
In Classic mode (or Low Density) operation, the 2500C-8-TC operates logs in to the PLC as
an 8 word Input (8WX) module. Temperature values for each channel are reported to the
PLC in the corresponding input word. In Classic mode, the module accepts Type J
Thermocouple range. To operate the module in other ranges, you must change to Classic
Plus mode.
1.4.1.1 Classic Mode Module Default Configuration
The 2500C-8-TC ships in a default configuration which matches a common set of
application requirements.
2500-8-TC Default Shipment Settings
Operation Mode
Classic Mode
Logon
8WX
Thermocouple
J
Digital Filtering
Enabled
Scaling
Enabled
Temperature Units
Degrees C
Figure 3 2500C-8-TC Default Configuration Table
1.4.2 Classic Plus Mode
In Classic Plus mode (or High Density) operation, the 2500-8-TC operates logs in to the PLC
as an 8 word input / 8 word output (8WX/8WY) module. Thermocouple or millivolt signal
values for each channel are reported to the PLC in the corresponding input word. The WY
output words are used to allow the PLC to select the input signal range for the module.
For example, if the module is in Classic Plus mode and is logged in at address 1:
WX1 = Channel 1 TC/mV Input
WY9 = Channel 1 Configuration
WX2 = Channel 2 TC/mV Input t
WY10 = Channel 2 Configuration
WX3 = Channel 3 TC/mV Input
WY11 = Channel 3 Configuration
WX4 = Channel 4 TC/mV Input
WY12 = Channel 4 Configuration
WX5 = Channel 5 TC/mV Input
WY13 = Channel 5 Configuration
WX6 = Channel 6 TC/mV Input
WY14 = Channel 6 Configuration
WX7 = Channel 7 TC/mV Input
WY15 = Channel 7 Configuration
WX8 = Channel 8 TC/mV Input
WY16 = Channel 8 Configuration
Figure 4 2500C-8-TC Classic Plus Login Table
In Classic Plus mode, the PLC can select range operation from any of the following by
setting the appropriate bits in the corresponding WY word for each channel. In addition, the
PLC can enable or disable digital filtering, Scaling enable or disable, Degrees C or Degrees
F for each channel.

2500C-8-TC Installation and Operation Guide
9
Figure 5 2500C-8-TC Classic Plus Configuration Options
1.5 Input Signal Ranges
Figure 6 2500C-8-TC Thermocouple Measurement Ranges
1.6 Measurement Resolution
The module has a resolution of approximately 0.1oC, 0.1oF or exactly .01 millivolts.
The chart below shows the corresponding input resolution per step for each of the input
configuration modes:
Thermocouple
mVolt
J, K, N, R
S*, T*, E*
0-55mV
*Note: S, T, E also require a jumper selection change from
the shipped jumper configuration per channel.
Thermocouple Measurement Ranges
J: -210ºC to 760ºC (-350ºF to 1400ºF)
K: -270ºC to 1372ºC (-450ºF to 2500ºF)
T: -270ºC to 400ºC (-454ºF to 752ºF)
E: -270ºC to 1000ºC (-454ºF to 1832ºF)
R: 0ºC to 1768ºC (32ºF to 3214ºF)
S: 0ºC to 1768ºC (32ºF to 3214ºF)
N: -260ºC to 1300ºC (-436ºF to 2372ºF)
mV: -55 to +55mV

2500C-8-TC Installation and Operation Guide
10
1.7 Accuracy
The module measurement accuracy is listed below for each Thermocouple Type and
millivolt signals:
Figure 7 2500C-8-TC Accuracy Rating Table
1.8 Digital Word map
Thermocouple and/or millivolt signals are translated into a 15-bit plus sign digital word.
Since the PLC requires a 16-bit input word, the 15-bit value from the converter is placed into
a 16-bit word for transmittal to the PLC, the extra bit being used to show the sign of the
value.
The data is reported to the PLC in the format shown below:
Sign bit 16,384 8192 4096 2048 1024 512 256 128 64 32 16 8 4 2 1
Figure 8 2500C-8-TC Digital Word Map Diagram
In addition to applying a basic scale of 0-32000, the module provides a over-range error
value of 32765 or under-range error value of 32766.
Accuracy :
Thermocouple Types and mV
J : +/-1ºC from 0ºC to 60ºC
K: +/-1ºC from 0ºC to 60ºC
T: +/-1ºC from 0ºC to 60ºC
E: +/-1ºC from 0ºC to 60ºC
R: +/-2ºC from 0ºC to 60ºC*
S: +/-2ºC from 0ºC to 60ºC*
N: +/-1ºC from 0ºC to 60ºC
mV: +/-0.5% full scale or +/- 500µV
* reduced accuracy for measurements
below 500ºC

2500C-8-TC Installation and Operation Guide
11
1.9 Thermocouple Input to Digital Conversion
1.9.1 Scaling Enabled
When module SCALING is enabled, data is reported as engineering units to the PLC as
follows:
Thermocouple Mode, digital word (WX) = Degrees x 10
Millivolt Mode, digital word (WX) = -10,000 to +10,000
As an example, the following Figure 1.3 illustrates the effects of a change in input level
going from 0 to 102.4oF in the Thermocouple Input Mode.
Example 1: 0.0oF = (Digital Word (WX))/10
MSB
LSB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.
.
.
.
.
.
.
.
.
.
32
16
8
4
2
1
Example 2: 102.4oF = (Digital Word (WX))/10
MSB
LSB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
.
.
.
.
1024
.
.
.
32
16
8
4
2
1
Figure 9 2500C-8-TC Example of Change in Input Level
1.9.2 Scaling Disabled
When data format is selected as SCALING disabled the full temperature range of the
thermocouple is reported as an unsigned integer from 0 to 32000 for thermocouple units or
–32,000 to +32,000 for mV units (range of +/-55mV). The following formulas may be used to
calculate the scaled integer value for temperature and mV.
Temperature: Scaled Integer = (measured temp - min temp) / (max temp - min temp) x
32000 example: the scaled integer offset at 0oC for a Type J thermocouple is:
Scaled integer = (0 - (-210)) / (760 - (-210)) x 32000 = 6928
example: the scaled integer overrange at 770oC for a Type J thermocouple is:
Scaled integer = (770 - (-210)) / (760 - (-210)) x 32000 = 32330
mV: Scaled Integer = mV x (32,000 ÷ 55)
example: the scaled integer offset at 20 mV is:
Scaled Integer = 20 x (32,000 ÷ 55) = ~11636.36

2500C-8-TC Installation and Operation Guide
12
The table below shows the scaling temperature ranges of each probe type.
Probe Type
Temperature Range
oC
oF
J
-210 to 760
-346 to 1400
K
-220 to 1320
-364 to 2408
T
-230 to 400
-382 to 752
E
-240 to 700
-400 to 1292
R
0 to 1768
32 to 3214
S
0 to 1768
32 to 3214
N
-200 to 1300
-328 to 2372
Figure 10 2500C-8-TC Example of Change in Input Level
1.10 Effect of Out-of-Range Input Signals
The 2559-TC utilizes the underrange and overrange codes of 32766 and 32765,
respectively, to indicate when a channel has reached individual limits. Thermocouple inputs
exceeding the ANSI standard for the different types of thermocouples (listed on the following
pages in Figures 1.4-1.11) will cause the overrange value, 32765, to be displayed and the
maximum temperature for that thermocouple type to be returned. Open thermocouples
report temperatures that are out of the allowable range. This condition may occur due to
failure of the thermocouple or due to the thermocouple wire being cut or disconnected. The
2559-TC will report an open thermocouple condition within 200 milliseconds.
NOTE:
The 2559-TC uses the overrange error code, 32765, to indicate an open thermocouple. An open
thermocouple condition will report within 200 milliseconds.
Figure 11 2500C-8-TC Effect of Voltage Input on Type J Thermocouple

2500C-8-TC Installation and Operation Guide
13
Figure 12 2500C-8-TC Effect of Voltage Input on Type J Thermocouple
Figure 13 2500C-8-TC Effect of Voltage Input on Type T Thermocouple
Figure 14 2500C-8-TC Effect of Voltage Input on Type E Thermocouple
Figure 15 2500C-8-TC Effect of Voltage Input on Type R Thermocouple

2500C-8-TC Installation and Operation Guide
14
Figure 16 2500C-8-TC Effect of Voltage Input on Type S Thermocouple
Figure 17 2500C-8-TC Effect of Voltage Input on Type N Thermocouple
Figure 18 2500C-8-TC Effect of Voltage Input on mV Input

2500C-8-TC Installation and Operation Guide
15
1.11 Error Code Values Reported to the PLC
The ‘temperature sensor bad’ code is reported to the PLC when either of the two
temperature sensors encapsulated in front panel connector goes bad. This is a rare
occurrence, but would yield code 32,761 if it does occur.
The math overflow code of 32,763 occurs when the thermocouple type, mV and SCALE
modes are chosen, and the units tries to report a value under –32,000.The following chart
summarizes the 2500C-8-TC error codes:
Error Code
Error
Comment; Corrective Action
32761
Bad Temperature
Sensor(s)
A temperature sensor (s) in front panel
connector is faulty/defective; call CTI for
replacement 2500C-8-TC connector, P/N:
2500C-32F-CJC.
32763
Math Overflow
Low end range of mV/SCALE exceeded;
Check process to determine if input is actually
low. Determine if mV transmitter is defective.
32764
EEPROM Error
EEPROM Storage Error
32765
Channel Overrange
Input level is above normal input range (see
Figures 1.4-1.11 for each thermocouple type);
Check process to determine if input is actually
high or if the transmitter is defective.
32766
Channel Underrange
Input level is above below input range (see
Figures 1.4-1.11 for each thermocouple type);
Check process to determine if input is actually
low or if the transmitter is defective.
Figure 19 2500C-8-TC Error Code Table

2500C-8-TC Installation and Operation Guide
16
1.12 Module Setup from the PLC in Classic Plus Mode
When operating in Classic Plus Mode, the module reads setup information that the PLC has
stored in the WY word corresponding to each channel. See Section 1.4.2 for module log on
example.
Figure 20 2500C-8-TC Word Map for Configuration Data
Bit 1 –Sets Temperature Measurement Range to Degrees Centigrade or Fahrenheit
0=Centigrade 1=Fahrenheit
Bit 2 –Sets Digital Filtering Enabled or disabled
0=Enabled 1=Disabled
Bit 3 –Sets Scaling Mode Enabled or Disabled
0=Enabled 1=Disabled
Bit 4 and Bit 5 are not used
Bit 6 through Bit 8 are used to set the input channel to millivolt ranges or select the
Thermocouple Type
000 = 55 millivolts
001 = Type E Thermocouple
010 = Type J Thermocouple
011 = Type K Thermocouple
100 = Type N Thermocouple
101 = Type R Thermocouple
110 = Type S Thermocouple
111 = Type T Thermocouple
Binary Examples of the Configuration Word for WY9 (Channel 1) X represents a null location
000x x000 xxxx xxxx
Module is set for ºC, Digital Filtering, Scaling Enable, 55mV
100xx001 xxxx xxxx
Module is set for ºF, Digital Filtering, Scaling Enable, Type E
100x x010 xxxx xxxx
Module is set for ºF, Digital Filtering, Scaling Enable, Type J
Figure 21 2500C-8-TC Binary Example of Module Configuration Word
MSB
LSB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.
.
.
Not Used
.
.
.
Bit 9 through 16 Not Used

2500C-8-TC Installation and Operation Guide
17
CHAPTER 2 INSTALLATION & SETUP
The installation of the 2500C-8-TC consists of the following steps:
1) Reading this Chapter
2) Installation planning
3) Unpacking the module
4) Configuring the module
5) Physical installation
6) Connecting field wiring
7) Checking operation
2.1 Installation Planning
2.1.1 Safety Considerations
Before installing the module, you must identify the personnel hazards that may be created in
the event of a system failure and provide interlocks and safety switches to prevent operation
during a system failure. Refer to the NEMA ICS 3-304 Programmable Control Standards.
WARNING
As a system designer, you should be aware that Control devices can fail in an unsafe condition. Unless
you incorporate proper safeguards, malfunction of the controller or associated devices, such as
operator interface equipment, could cause sudden equipment startup, shutdown, or other unexpected
operation. Such startup or shutdown or unexpected operation could result in death or serious injury to
personnel, and/or damage to equipment.
If you or your company are using CTI controllers with equipment that requires the presence of a person
(such as an operator or attendant), you should be aware of this potential safety hazard and take
appropriate precautions.
The precautions below conform to the National Electrical Manufacturers Association
guidelines for installation of programmable controllers as recommended in the NEMA ICS 3–
304 Programmable Control Standards.
ICS 3-304.81 Safety Recommendations:
Consideration should be given to the use of an emergency stop function which is
independent of the programmable controller. Where the operator is exposed to the
machinery, such as in loading or unloading a machine tool, or where the machine cycles
automatically, consideration should be given to the use of an electromechanical override or
other redundant means, independent of the programmable controller, for starting and
interrupting the cycle. If provision is required for changing programs while the equipment is
in operation, consideration should be given to the use of locks or other means of assuring
that such changes can be made only by authorized personnel. These recommendations are

2500C-8-TC Installation and Operation Guide
18
intended as safeguards against the failure of critical components and the effects of such
failures or the inadvertent errors that might be introduced if programs are changed while the
equipment is in operation.
Operator Safety Switches
Power should be configured so that it can be manually removed from all output devices. You
must provide a method that is independent of the control system for disconnecting power
from the outputs when a machine is not operating or the operator must reach into the
machine. A non-electronic switch or directly wired relay must be used to disconnect the
power.
Emergency Stop Switch
You must provide a method for disconnecting power from the outputs if an emergency
situation is encountered with the machine operation. Use a non-electronic switch or relay
that is wired external to the controller and that is easily accessible.
2.1.2 Electrical Interference
Electrical interference can adversely affect the operation of control equipment. The major
sources of electrical interference in an industrial environment are devices that use high
voltages and current, such as motors and welders. Electrical interference can be conducted
directly through wiring or inducted via electromagnetic coupling.
To ensure a reliable control system, you will need to determine the source of the electrical
interference and employ suitable techniques to eliminate it.
2.1.3 Grounding
It is very important that the all equipment is properly grounded. Lack of proper grounding
may cause intermittent or erratic operation or may cause the control system to fail. A
properly installed grounding system will provide a low-impedance path to earth ground,
which will give all PLC internal filtering devices a good ground return for reference. The
earth ground of the building site typically provides reliable grounding; however, if excessive
ground current is present, a separate grounding electrode should be installed.
A common practice is to provide a central ground bus bar as a single point of reference
within each enclosure, connecting all chassis and power supply components to the bus bar.
The bus bar is then connected to earth ground. When connecting to the bus bar, use 1 inch
copper braid or No. 8 AWG wire. To ensure good connections, scrape paint or other non-
conductive coatings away from mounting studs and from enclosure surfaces where
mounting bolts and washers make contact.
In addition to connecting the controller rack and power supply to earth ground, you must
ensure that the power supply, controller and all modules installed in the base are installed
securely and that the thumbscrews are tightened.