FW MURPHY RTDT Series RTD Transmitter Installation Guide

FW MURPHY RTDT Series RTD Transmitter

Product Information

• Product Name: RTD Transmitter
• Model: RTDT Series
• Manufacturer: FW MURPHY

Specifications

• Power Supply Voltage (Min ): 24 VDC
• Resistive Load (Max ): 550 ohm
• Terminal Strip Wire Gauge : 14 to 22 gauge
• Supply Voltage Range: 13-40 VDC

Product Usage Instructions

1. Inspect the product for any shipping damage before installation.
2. Hire a qualified person to install the RTD Transmitter and ensure it conforms to NEC and local codes.
3. Ensure the power supply voltage meets the minimum requirement of 24 VDC.
4. Do not connect power to the RTD input or the RTD itself.
5. Use copper wire for the terminal strip on the transmitter. Special compensation wire is not required.
6. Route all transmitter wiring in separate conduit to isolate it from high voltage or high current carrying lines.
7. For the 4-20 mA signal, use shielded wire.
8. Refer to the Loop Resistance Graph to determine the appropriate load resistance (RL) based on the supply voltage (VDC).
9. To recalibrate the RTDT, follow these steps
   • Use a precision RTD simulator with a traceable calibration.
   • Adjust the zero potentiometer for 4.0 mA output using a resistance value corresponding to the temperature at 4.0 mA.
   • Adjust the Rlin potentiometer for 12.0 mA output using a resistance value corresponding to the temperature at 12.0 mA.
   • Adjust the span potentiometer for 20.0 mA output using a resistance value corresponding to the temperature at 20.0 mA.
   • The zero, Rlin, and span adjustments are interactive, so repeat steps b, c, and d as necessary.

Note: The product specifications and designs are subject to change without notice.

Installation of RTD Transmitter

Models: RTDT Series
Please read the following information before installing. Visually inspect this product for any shipping damage. It is your responsibility to have a qualified person install this unit and make sure it conforms to NEC and local codes.
The FW Murphy RTD transmitter is designed to accept a signal from an RTD sensing element, and to provide a linearized 4 to 20 mA output current. The output cur rent is directly proportional to the temperature of the RTD temperature sensor. Since the temperature is converted to a current signal, voltage drops in the power supply leads to the transmitter have no effect on the integrity of the signal. As long as the transmitter has sufficient DC voltage at its terminals, it will produce a cur rent linearly proportional to temperature. This means that the transmitter may be remote mounted but should be near the sensor, reducing the effects of noise and minimizing errors due to long leads on the RTD sensor. The RTD instruments have screw terminal connections and accept 2 or 3 wire RTD’s*. They include high resolution, 24-turn zero and span potentiometers and each unit is calibrated after a minimum of 48 hours burn-in and checkout time.

WARNING
BEFORE BEGINNING INSTALLATION OF THIS PRODUCT Disconnect all electrical power to the machine Make sure the machine cannot operate during installation Follow all safety warnings of the machine manufacturer Read and follow all installation instructions

Specifications

• Sensor Input : Platinum RTD 100 ohms
• Output Span : 4 to 20 mA
• Loop Power Supply Voltage : Typically 24 VDC; when using Loop Resistance Graph 13 – 40 VDC.
• Temperature Span : 50° F (28° C) minimum; l000° F (556° C) maximum Calibrated Accuracy: 0.1 %
• Conformity : 0.1 % of Span
• Ranges : -60 to 140° F; 0 to 400° F
• Ambient Temperature Limits : -30 to 165° F (-34 to 74° C)
• Power Supply Effect : 0.001 % volt
• Current : 3.4 mA minimum; 30 mA maximum.
• Upscale Burnout : Standard
• Reversed Polarity Protection : Standard
• Nominal Zero and Span Adjustments : ±10%
• Connections : Screw Terminal
• Power Supply

Transmitters are designed for a nominal 24 VDC power supply. They will operate with a 13 to 40 VDC supply at the transmitter power supply terminals. Use the following formulas to determine maximum resistive loading (RL) allowed for the power supply used, or to deter-mine minimum supply voltage M required for fixing resistive loads. Formulas assume a maximum current of 20 mA.

NOTE: Devices such as FW Murphy’s EMS Series controllers, 400 and 500 Series PLC controllers, and the RMUJ 6 have 250 ohms resistors that add to the resistive loading.

Power Supply Voltage (Min) Resistive Load (Max)
V = (0.02 A x RL) + 13 V RL = (V – 13) /0.02

Example: Example

• 550 ohm load 24 VDC power supply
• V = 0.02 x 550 + 13 RL = (24 V – 13 V) /0.02
• V = 24 VDC minimum power supply RL = 550 ohm maximum

Dimensions

NOTE: Slot accepts 6-32 screw

Wiring
CAUTION: Do Not connect power to the RTD input. Do Not connect power to the RTD itself. Do Not use AC line power.

The terminal strip on the transmitter accepts 14 to 22 gauge wires. Copper wire is to be used since special compensation wire is not required. Route all transmitter wiring in separate conduit to isolate it from high voltage or high current carrying lines. It is also recommended that shielded wire be used for the 4-20 mA signal.

Loop Resistance Graph
Supply voltage for the RTDT must be within 13-40 VDC. The figure below shows the minimum supply voltage (VDC) required for a given load resistance (RL).

In order to consistently bring you the highest quality, full-featured products, we reserve the right to change our specifications and designs at any time.
FW MURPHY product names and the FW MURPHY logo are proprietary trademarks. This document, including textual matter and illustrations, is copyright protected with all rights reserved. (c) 2021 FW MURPHY. A copy of our typical warranty may be viewed or printed by going to www.fwmurphy.com/warranty.

Installation

Open Sensor Indication
When an RTD has failed due to an open sensor (broken path in the element), the transmitter will indicate an error. The way the error is produced is by driving the current high, above 20 mA (upscale burn-out). However, the burnout indication does not apply to breaks in the lead compensation loop.

Application Hints
The calibrated output of the FW Murphy Transmitter is 4.0 to 20.0 mA. However, the lower and upper limit of output current is approximately 3.4 and 30 mA respectively. This means that for the system using a 250 ohm resistor (1 to 5 V), the maximum voltage could be as high as 7.5 voles (30 mA x 250 ohms) in the case of an open RTD. Some computer-based systems will not tolerate input voltages greater than approximately 5.5 volts. Instead of selecting a different scaling resistor (167 ohms for example gives 5 V for an open RTD), a 5.1 V zener diode in parallel with the scaling resistor will clamp the voltage across the scaling resistor to 5.1 V while still allowing the calibrated range to remain 1 to 5 voles. See figure below.

The transmitter dissipates power according to the formula : Power = Volts x Amps. The dissipated power is equal to the voltage at
the transmitter’s terminals multiplied by the operating current. A transmitter with 24 voles at its terminal and with maximum current (30 mA for an open RTD) will dissipate 0.7 watts of power. This can be significant if the RTD sensor can be affected by thermal gradients from the transmitter.

RTDT Calibration
FW Murphy RTD transmitter modules are factory calibrated. Please DO NOT attempt to recalibrate unless the proper equipment is avail-able. If recalibra tion is necessary, a Zero, Rlin, and Span adjustment can be made from the top of the unit. A precision RTD simulator with a traceable calibration must be used. Consult a book of tables for resistance values.

1. With a resistance value corresponding with the temperature at 4.0 mA, adjust the zero potentiometer for 4.0 mA output.
2. With a resistance value corresponding with temperature at 12.0 mA, adjust the Rlin potentiometer for 12.0 mA output.
3. With a resistance value corresponding with the temperature at 20.0 mA, adjust the span potentiometer for 20.0 mA output.
4. The zero, Rin and span adjustments are interactive. Repeat steps 1, 2, and 3 as necessary.

Example 1

1. If range equals 50 – 250°, then span equals 200°
2. Divide 200° by 2: 200° + 2 = 100°
3. Add 100° to lower end of range : 50° + 100° = 150°
4. 50° equals the Zero point (4 mA)
5. 150° equals 50% of the Span (12 mA) (Rlin)
6. 250° equals the Span point (20 mA)

Example 2

1.  Set zero at 4.0 mA for -100° F (70.95 Q)
2.  Set Rin at 12.0 mA for 0° F (93.01 Q)
3. Set span at 20.0 mA for l00° F (114.68 Q)

Troubleshooting

• Current loop open at some point
• No voltage out at power supply
• Wrong polarity on loop supply

Current over 20 mA|

• RTD is open
• Current loop connections shorted

__ Erratic readings|

• Loose connection in RTD or signal loop
• Damaged RTD
• AC noise on loop connections
• Exceeds loop resistance R

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References

• Warranty & Terms of Sale - FW Murphy Production ControlsFW Murphy Production Controls

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