National Instruments Network Router cFP RTD 124 User Manual

FieldPoint Operating Instructions  
FP-RTD-124  
AND CFP-RTD-124  
Eight-Channel Four-Wire RTD  
and Resistance Input Modules  
These operating instructions describe how to install and use the  
National Instruments FP-RTD-124 and cFP-RTD-124 three-wire  
RTD and resistance input modules (referred to inclusively as the  
[c]FP-RTD-124). For details on configuring and accessing the  
[c]FP-RTD-124 over a network, refer to the user manual for the  
FieldPoint network module you are using.  
Features  
The [c]FP-RTD-124 is a FieldPoint RTD and resistance input  
module with the following features:  
Inputs for 100 platinum RTDs (resistance temperature  
detectors)  
Built-in linearization for six TCR (temperature coefficient of  
resistance, or alpha) values of RTDs  
Direct resistance measurements with a 400 range  
Four-wire measurement for high accuracy  
16-bit resolution  
Filtering against 50 and 60 Hz noise  
2,300 Vrms transient overvoltage protection  
–40 to 70 °C operation  
Hot plug-and-play  
FieldPoint™, National Instruments™, NI™, and ni.com™ are trademarks of National Instruments Corporation.  
Product and company names mentioned herein are trademarks or trade names of their respective companies.  
For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software,  
the patents.txt file on your CD, or ni.com/patents.  
323349A-01  
October 2002  
© 2002 National Instruments Corp. All rights reserved.  
 
To install the cFP-RTD-124, refer to Figure 2 and complete the  
following steps:  
1. Align the captive screws on the cFP-RTD-124 with the holes  
on the backplane. The alignment keys on the cFP-RTD-124  
prevent backward insertion.  
2. Press firmly to seat the cFP-RTD-124 on the backplane.  
3. Using a number 2 Phillips screwdriver with a shank of at least  
64 mm (2.5 in.) length, tighten the captive screws to 1.1 N m  
(10 lb in.) of torque. The nylon coating on the screws  
prevents them from loosening.  
5
2
1
4
5
4
3
1
2
cFP Backplane  
cFP Controller Module  
3
4
cFP I/O Module  
Captive Screws  
5
Screw Holes  
Figure 2. Installing the cFP-RTD-124  
© National Instruments Corp.  
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FP-RTD-124 and cFP-RTD-124  
 
 
Wiring the [c]FP-RTD-124  
The FP-TB-x terminal bases have connections for each of the eight  
input channels on the FP-RTD-124. The cFP-CB-x connector  
blocks provide the same connections for the cFP-RTD-124.  
Table 1 lists the terminal assignments for the signals associated  
with each channel.  
Table 1. Terminal Assignments  
Terminal Numbers  
Channel  
SENSE+  
SENSE–  
EXCITE+  
COM  
18  
0
1
2
3
4
5
6
7
1
3
2
4
17  
19  
21  
23  
25  
27  
29  
31  
20  
5
6
22  
7
8
24  
9
10  
12  
14  
16  
26  
11  
13  
15  
28  
30  
32  
If you are using shielded wiring, you can reduce input signal noise  
by connecting one end of the shield to the COM terminal. Do not  
connect the shield to any of the wires at the signal end.  
Taking RTD Measurements  
with the [c]FP-RTD-124  
The [c]FP-RTD-124 has eight input channels. All eight channels  
share a common ground that is isolated from other modules in the  
FieldPoint system. Each channel pulses a 2 mA excitation current  
out of the EXCITE+ terminal. The excitation current returns  
through the COM terminal. The SENSE+ and SENSEterminals  
measure resistance and compensate for lead resistance errors. Each  
channel is filtered, then sampled by a 16-bit analog-to-digital  
converter.  
FP-RTD-124 and cFP-RTD-124  
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Figure 3 shows the input circuitry on one channel.  
Pulsed 2 mA  
EXCITE+  
SENSE+  
Amplifier  
16-bit  
ADC  
Four-Wire  
RTD  
SENSE–  
COM  
[c]FP-RTD-124  
Figure 3. FP-RTD-124 Input Circuit  
Taking Measurements from Four-Wire RTDs  
Four-wire RTDs generally have two wires of one color and two of  
another color (usually red and white). Connect the wires of one  
color to the positive terminals (EXCITE+ and SENSE+). Connect  
the wires of the other color to the negative terminals (COM and  
SENSE).  
EXCITE+  
SENSE+  
Four-Wire  
RTD  
SENSE–  
COM  
[c]FP-RTD-124  
Figure 4. Four-Wire RTD Connections on One Channel  
Taking Measurements from Three-Wire RTDs  
NI recommends the [c]FP-RTD-122 for three-wire RTD  
measurements because it includes special sensing circuitry to  
compensate for up to 95% of the lead resistance of the third wire.  
Most three-wire RTDs have two wires of one color (usually red,  
sometimes black) and one wire of another color (usually white,  
sometimes red). Connect the two wires of the same color to the  
© National Instruments Corp.  
5
FP-RTD-124 and cFP-RTD-124  
 
 
negative terminals (COM and SENSE). Connect the third wire to  
the positive terminal (SENSE+). Use a short jumper wire to  
connect the EXCITE+ terminal to the SENSE+ terminal.  
Short Jumper Wire  
EXCITE+  
SENSE+  
Three-Wire  
RTD  
SENSE–  
COM  
[c]FP-RTD-124  
Figure 5. Three-Wire RTD Connections on One Channel  
Taking Measurements from Two-Wire RTDs  
Connect one wire of a two-wire RTD to the SENSE+ terminal and  
the other wire to the SENSEterminal. Use a short jumper wire to  
connect the SENSE+ terminal to the EXCITE+ terminal. Use  
another short jumper wire to connect the SENSEterminal to the  
COM terminal.  
Short  
Jumper  
Wire  
EXCITE+  
SENSE+  
Two-Wire  
RTD  
SENSE–  
COM  
Short  
Jumper  
Wire  
[c]FP-RTD-124  
Figure 6. Two-Wire RTD Connections on One Channel  
FP-RTD-124 and cFP-RTD-124  
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Measuring Resistance  
You can use the [c]FP-RTD-124 to measure resistance in ohms.  
In this way, you can take measurements from RTDs of types that  
the [c]FP-RTD-124 does not directly support (such as 120 nickel  
RTDs) and from resistive devices other than RTDs. You can  
measure resistances up to 400 . Resistance values greater than  
400 , including open circuits, result in an Out of rangeerror  
for the affected channels. The [c]FP-RTD-124 ignores any  
configuration of RTD type for channels with resistance selected.  
Converting Resistance Measurements  
to Temperature Measurements  
The [c]FP-RTD-124 has built-in linearization algorithms for  
platinum RTDs of either 100 or 1,000 nominal resistance,  
and for 6 TCR (or alpha, α) values. The TCR is the average  
temperature coefficient of resistance of an RTD from 0 to 100 °C.  
This document specifies TCR in units of m/Ω/°C.  
The [c]FP-RTD-124 linearizes resistance values and returns  
readings in units of temperature. The available ranges are 73 to  
1,123 K, 200 to 850 °C, and 328 to 1,562 °F. You can configure  
each channel independently, so you can connect different types of  
RTDs to each channel.  
Note You must configure each channel of the  
[c]FP-RTD-124 for the type of RTD connected to it.  
The module does not automatically recognize RTD types.  
RTD Types  
RTD types are specified by material composition, nominal  
resistance at 0 °C, and TCR. The [c]FP-RTD-124 can directly  
measure the temperature of platinum RTDs of 100 nominal  
resistance. These RTDs are commonly referred to as PT100 RTDs.  
Different types of platinum RTDs have different TCRs. The  
[c]FP-RTD-124 supports the following TCRs: 3.750, 3.851, 3.911,  
3.916, 3.920, and 3.928 m/Ω/°C. The most common TCR for  
RTDs is 3.851 m/Ω/°C. It is defined in international standards  
such as IEC-751, DIN 43760, BS 1904, and ASTM E1137. The  
TCR of 3.928 m/Ω/°C is used in the reference function for  
platinum thermometers in the International Temperature Scale  
of 1990 (ITS-90) for high-accuracy metrology applications.  
© National Instruments Corp.  
7
FP-RTD-124 and cFP-RTD-124  
 
Unfortunately, not all TCR values are as well defined by standards  
organizations, and the behavior of RTDs with the same TCR value  
may vary from vendor to vendor. The variations are usually small,  
and the built-in linearization algorithms of the [c]FP-RTD-124 are  
appropriate for nearly all applications.  
The [c]FP-RTD-124 uses a linearization curve known as the  
Callendar-Van Dusen equation to measure the temperature of  
RTDs. The equation is as follows:  
Temperatures below 0 °C:  
RT = R0[1 + A × T + B × T2 + C × T3 × (T 100 °C)]  
Temperatures above 0 °C:  
RT = R0[1 + A × T + B × T2]  
T = temperature in °C  
RT = RTD resistance at temperature T  
R0 = RTD nominal resistance at 0 °C  
A, B, and C are coefficients given in Table 2.  
Table 2 lists the coefficients used in this equation for each of the  
TCR values that the [c]FP-RTD-124 supports. If you have a  
nonstandard RTD that does not match one of these linearization  
curves, measure the resistance with the [c]FP-RTD-124 and  
convert the resistance to temperature in the manner suggested by  
the RTD vendor.  
Table 2. Callendar-Van Dusen Coefficients Used by the [c]FP-RTD-124  
A
(°C)1  
B
(°C)2  
C
(°C)4  
TCR  
m//°C  
3.750  
3.851  
3.911  
3.916  
3.920  
3.928  
3.81 × 103  
3.9083 × 103  
3.9692 × 103  
3.9739 × 103  
3.9787 × 103  
3.9888 × 103  
6.02 × 107  
5.775 × 107  
5.8495 × 107 4.233 × 1012  
5.870 × 107 4.4 × 1012  
5.8686 × 107 4.167 × 1012  
5.915 × 107 3.85 × 1012  
6.0 × 1012  
4.183 × 1012  
FP-RTD-124 and cFP-RTD-124  
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Effects of Lead Resistance  
The [c]FP-RTD-124 measures resistance by driving a current  
through a circuit and sensing the resulting voltage. Any resistance  
in the lead wires that connect to the RTD can add errors to your  
readings if the measured voltage includes the drop across these  
wires.  
For example, consider a two-wire RTD element connected as  
previously shown in Figure 2. The resistance of the lead wires is  
indistinguishable from the resistance of the RTD element. In a  
typical application using 10 m of 22 AWG copper wire, each of the  
two leads adds approximately 0.5 of error to the measurement.  
The 0.5 of error corresponds to a temperature error of about  
2.6 °C. Using the three-wire RTD connection in Figure 2 causes  
the inclusion of only one of the leads in the sensed measurement.  
The resultant error caused by lead resistances is half that of the  
error in the two-wire example.  
The most accurate way to measure temperature from RTDs is the  
four-wire method shown in Figures 2 and 3. With this method, one  
pair, the EXCITE and COM leads, carries the current through the  
RTD. The other pair, the SENSE leads, measures the voltage  
developed by the RTD element independent of the lead resistance.  
Status Indicators  
The [c]FP-RTD-124 has two green status LEDs, POWER and  
READY. After you insert the [c]FP-RTD-124 into a terminal base  
or backplane and apply power to the connected network module,  
the green POWER indicator lights and the [c]FP-RTD-124  
informs the network module of its presence. When the network  
module recognizes the [c]FP-RTD-124, it sends initial  
configuration information to the [c]FP-RTD-124. After receiving  
this initial information, the green READY indicator lights and the  
[c]FP-RTD-124 is in normal operating mode.  
Isolation and Safety Guidelines  
Caution Read the following information before  
attempting to connect the [c]FP-RTD-124 to any circuits  
that may contain hazardous voltages.  
This section describes the isolation of the [c]FP-RTD-124 and its  
compliance with international safety standards. The field wiring  
© National Instruments Corp.  
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FP-RTD-124 and cFP-RTD-124  
 
connections are isolated from the backplane and the inter-module  
communication bus. The isolation is provided by the module,  
which has optical and galvanic isolation barriers designed and  
tested to protect against transient fault voltages of up to 2,300 Vrms  
.
Follow these guidelines to ensure a safe total system:  
The [c]FP-RTD-124 has a safety isolation barrier between the  
I/O channels and the inter-module communication bus. There  
is no isolation between channels unless otherwise noted. If any  
of the channels on a module are wired at a hazardous potential,  
make sure that all other devices or circuits connected to that  
module are properly insulated from human contact.  
Do not share the external supply voltages (the V and C  
terminals) with other devices (including other FieldPoint  
devices), unless those devices are isolated from human contact.  
For Compact FieldPoint, you must connect the protective earth  
(PE) ground terminal on the cFP-BP-x backplane to the system  
safety ground. The backplane PE ground terminal has the  
following symbol stamped beside it: . Connect the  
backplane PE ground terminal to the system safety ground  
using 14 AWG (1.6 mm) wire with a ring lug. Use the 5/16 in.  
panhead screw shipped with the backplane to secure the ring  
lug to the backplane PE ground terminal.  
As with any hazardous voltage wiring, make sure that all  
wiring and connections meet applicable electrical codes and  
commonsense practices. Mount terminal bases and backplanes  
in an area, position, or cabinet that prevents accidental or  
unauthorized access to wiring that carries hazardous voltages.  
Operate the [c]FP-RTD-124 only at or below Pollution  
Degree 2. Pollution Degree 2 means that only nonconductive  
pollution occurs in most cases. Occasionally, however, a  
temporary conductivity caused by condensation must be  
expected.  
Refer to the FieldPoint product label for regulatory  
certification under hazardous location standards. If the  
FieldPoint product is not certified for operation in hazardous  
locations, do not operate it in an explosive atmosphere or  
where there may be flammable gases or fumes.  
FP-RTD-124 and cFP-RTD-124  
10  
ni.com  
 
Specifications  
These specifications are typical for the range 40 to 70 °C unless  
otherwise noted.  
Input Characteristics  
Number of channels..........................8  
ADC resolution.................................16 bits  
Type of ADC.....................................Delta-sigma  
Input signal ranges (software-selectable by channel)  
Temperature................................73 to 1123 K  
200 to 850 °C  
328 to 1562 °F  
Resistance...................................0 to 400 Ω  
Temperature accuracy  
Error  
15 to 35 °C  
40 to 70 °C  
Measured Value  
200 to 150 °C  
150 to 850 °C  
Typical  
Maximum  
0.25  
Typical  
Maximum  
0.60  
0.15  
0.25  
0.30  
0.80  
0.50  
1.50  
Resolution.........................................0.016 °C  
Resistance accuracy  
Offset error .................................0.03 typical, 0.1 max  
Gain error ...................................0.06% typical, 0.1% max  
Resolution...................................0.0061 Ω  
Excitation current..............................135 ms pulses of 2 mA every  
second  
Input noise ........................................ 1 bit peak-to-peak  
Signal input bandwidth.....................3 Hz  
Update rate........................................Each channel is updated  
once a second  
© National Instruments Corp.  
11  
FP-RTD-124 and cFP-RTD-124  
 
Physical Characteristics  
Indicators ..........................................Green POWER and  
READY indicators  
Weight  
FP-RTD-124...............................140 g (4.8 oz)  
cFP-RTD-124 .............................110 g (3.7 oz)  
Power Requirements  
Power from network module ............350 mW  
Isolation Voltage  
Channel-to-channel isolation............No isolation between  
channels  
Transient overvoltage........................2,300 Vrms  
Environmental  
FieldPoint modules are intended for indoor use only. For outdoor  
use, FieldPoint modules must be mounted inside a sealed  
enclosure.  
Operating temperature ...................... 40 to 70 °C  
Storage temperature.......................... 55 to 100 °C  
Humidity...........................................10 to 90% RH,  
noncondensing  
Maximum altitude.............................2,000 m  
Pollution Degree ...............................2  
Shock and Vibration  
Operating shock (IEC 68-2-27)  
cFP-RTD-124.............................. 50 g, 3 ms half sine, 3 shocks;  
30 g, 11 ms half sine,  
3 shocks  
Operating vibration, random (IEC 60068-2-34)  
FP-RTD-124...............................10500 Hz, 2.2 grms  
cFP-RTD-124 .............................10500 Hz, 5 grms  
Operating vibration, sinusoidal (IEC 60068-2-6)  
[c]FP-RTD-124...........................10500 Hz, 5 g  
FP-RTD-124 and cFP-RTD-124  
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Safety  
The [c]FP-RTD-124 is designed to meet the requirements of the  
following standards for safety and electrical equipment for  
measurement, control, and laboratory use.  
EN 61010-1, IEC 61010-1  
UL 3121-1  
CAN/CSA C22.2 No. 1010.1  
For certifications under regulatory standards, including hazardous  
location standards, refer to the product label or to ni.com.  
Electromagnetic Compatibility  
CE, C-Tick, and FCC Part 15 (Class A) Compliant  
Electromagnetic emissions ...............EN 55011 Class A at 10 m  
FCC Part 15A above 1 GHz  
Electromagnetic immunity................Evaluated to EN 61326:  
1997/A1: 1998, Table 1  
Note For full EMC compliance, you must operate this  
device with shielded cabling. Refer to the Declaration  
of Conformity (DoC) for this product for any additional  
regulatory compliance information. To obtain the DoC  
for this product, click Declaration of Conformity at  
ni.com/hardref.nsf/. Refer to the Read Me First  
document that accompanies the product for regulatory  
statements regarding FCC compliance.  
© National Instruments Corp.  
13  
FP-RTD-124 and cFP-RTD-124  
 
Mechanical Dimensions  
Figure 7 shows the mechanical dimensions of the FP-RTD-124  
installed on a terminal base. Dimensions are given in millimeters  
[inches]. If you are using the cFP-RTD-124, refer to the Compact  
FieldPoint controller user manual for the dimensions and cabling  
clearance requirements of the Compact FieldPoint system.  
107.19  
[4.22]  
109.5  
[4.31]  
91.44  
[3.60]  
Figure 7. FP-RTD-124 Mechanical Dimensions  
Where to Go for Support  
For more information about setting up your FieldPoint modular I/O  
system, refer to these National Instruments documents:  
FieldPoint network module user manual  
Other FieldPoint I/O module operating instructions  
FieldPoint terminal base operating instructions  
If you no longer have the print versions of these documents, you  
can find them online at ni.com.  
If you have searched the technical support resources on our Web  
site and still cannot find the answers you need, contact your local  
office or National Instruments corporate. For telephone support in  
the United States, dial 512 795 8248. For telephone support  
outside the United States, contact your local branch office:  
Australia 03 9879 5166, Austria 0662 45 79 90 0,  
Belgium 02 757 00 20, Brazil 55 11 3262 3599,  
Canada (Calgary) 403 274 9391,  
Canada (Montreal) 514 288 5722,  
Canada (Ottawa) 613 233 5949, Canada (Québec) 514 694 8521,  
Canada (Toronto) 905 785 0085, China 86 21 6555 7838,  
Czech Republic 02 2423 5774, Denmark 45 76 26 00,  
FP-RTD-124 and cFP-RTD-124  
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Finland 09 725 725 11, France 01 48 14 24 24,  
Germany 089 741 31 30, Greece 01 42 96 427,  
Hong Kong 2645 3186, India 91 80 4190000,  
Israel 03 6393737, Italy 02 413091, Japan 03 5472 2970,  
Korea 02 3451 3400, Malaysia 603 9596711,  
Mexico 001 800 010 0793, Netherlands 0348 433466,  
New Zealand 09 914 0488, Norway 32 27 73 00,  
Poland 22 3390 150, Portugal 210 311 210, Russia 095 238 7139,  
Singapore 65 6 226 5886, Slovenia 3 425 4200,  
South Africa 11 805 8197, Spain 91 640 0085,  
Sweden 08 587 895 00, Switzerland 056 200 51 51,  
Taiwan 02 2528 7227, United Kingdom 01635 523545  
© National Instruments Corp.  
15  
FP-RTD-124 and cFP-RTD-124  
 

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