Temperature transmitter Working principleA temperature transmitter is a device that connects to a temperature sensor to transmit the signal elsewhere for monitoring and control purposes. Typically, the temperature sensor is either an RTD, Thermisor or Thermocouple type sensor and will interface with a PLC, DCS, data logger or display hardware. The temperature transmitter’s role is to isolate the temperature signal, filter any EMC noise, amplify and convert the temperature sensor’s signal to a 4-20mA or 0-10V DC range for further use. 4-20ma temperature transmitters are common in manufacturing as the majority of industrial equipment communiciates via this signal range. The transmitted temperature signal can be scaled inside the temperature transmitter to accommodate the needs of the application, e.g. the 4mA can be used to represent -17.7°C (0° Fahrenheit) and the highest value in the range (20mA) can be used to represent 37.7° C (100° Fahrenheit)
Temperature transmitter types :-
There are tow types of temperature transmitter.
Head Type temperature Transmitter
Head Type temperature Transmitter :-
The compact head mounted temperature transmitter type is designed for standard sensor heads. The advantage increased measuring accuracy resulting from conversion of the sensor signal into a stable output signal close to the sensor. For thermocouple applications without compensation cables.
head mount temperature transmitters transform a temperature signal acquired from a Pt100, Pt1000 or Ni100 RTD sensor or from a thermocouple into a linearized 2-wire loop-powered 4 to 20 mA output. The characteristics of these converters ensure high precision on the reading scale with 16-bit conversion. The 4 to 20 mA output can be scaled based on the desired temperature input range.
Temperature Transmitter :-
temperature of a remote process must be monitored. Common temperature sensing devices such as thermocouples and RTD’s produce very small “signals.” These sensors can be connected to a two-wire transmitter that will amplify and condition the small signal. Once conditioned to a usable level, this signal can be transmitted through ordinary copper wire and used to drive other equipment such as meters, dataloggers, chart recorders, computers or controllers.
Input signals types for a temperature transmitterAn RTD (Resistance Temperature Detector or Resistance Temperature Device) is one of the most prevalent temperature sensors used in industry today. Also commonly referred to as PT100, its resulting popularity is due to its accuracy and repsonse at temperatures between -300 to + 600 ° F. The RTD sensor comprises of a resistor that changes value with temperature. The most common RTD by far is the PT100 385. This element measures 100 Ohms @ 0 degrees C (32 °F) and 138.5 Ohms @ 100 °C (212.0 °F). A thermomcouple sensor has a pair of dissimilar metal wires joined at one end. The junction produces a low level voltage proportional to the difference in temperature between the open and closed ends.
Advantages of temperature transmitters
Transmitters offer numerous advantages over the more traditional ways of measuring temperature.
- Ac power is not needed at the remote location to operate a twowire transmitter.
Since transmitters are powered by a low level 4-20 mA output current signal, no additional power has to be supplied at the remote location. In addition, the usual 24 Vdc signal necessary for operation is standard in plants that have large amounts of instrumentation.
- Electrical noise and signal degradation are not a problem for two-wire transmitter users.
The transmitter’s current output signal lends itself to a high immunity when it comes to ambient electrical noise. Any noise that does appear in the output current is usually eliminated by the common-mode rejection of the receiving device. In addition, the current output signal will not change (diminish) with distance as most voltage signals do.
- Wire costs drop significantly when using transmitters.
Low voltage signals produced by thermocouples almost always require the use of shielded cable when they are sent any significant distance. Ambient electrical noise from arcing electrical relays, motors and ac power lines can raise havoc with these signals that are transmitted in an unshielded cable. In addition, expensive, heavy gage wire is often installed in applications that call for long cable runs (since it reduces errors from signal voltage drops caused by line resistance).
- Ordinary copper wire can be used to connect all the pertinent equipment in a two-wire transmitter system. The 4-20 mA current output signal is relatively immune to ambient electrical noise and is not degraded by long distance transmission, even over a small diameter wire. Adding a temperature transmitter to a system eliminates the problem of having to provide long runs of costly wire and an extensive amount of shielding.
Temperature Transmitter Technical Specification :
|2.||Location||:||Tank no. 501|
|4.||TEMP. O C NOR/MAX||:||40 / 65|
OPERATING PRESSURE KG/CM2a
|7||W / T MATL.||:||S.S. 316|
|8||STEM LENGTH ‘L’||:||350 MM.|
THERMOWELL CONNECTION &
|:||1 1/2” ANSI 600 # RF|
|12||CASE AND COLOUR||:||MANUFACTURER STANDARD|
|13||ACCURACY||:||± 0 . 1 % , OR BETTER|
|14||MOUNTING||:||OTHER : 2” N.B. PIPE|
|15||ENCLOSURE CLASS||:||INTRINSICALLY SAFE FOR AREA CLASS – II A & B AS PER IEC.|
|16||ENERGY SUPPLY||:||24 V. D.C., 2 WIRE TRANSMITTER|
|17||INPUT||:||PT 100, 3 WIRE, CHARACTERISTICS AS PER DIN 43760|
|18||CHART DRIVE , CHART SPEED||:||—|
|19||TRANSMITTER OUTPUT||:||4 – 20 mA. DC. WITH SUPER IMPOSED DIGITAL SIGNAL AS PER HART PROTOCOL|
|20||SCALE||:||TYPE : LINEAR RANGES : 0 – 100O C|
Temperature Transmitter inspection plan and Test Plan
This content provides you with sample transmitter inspection and test plan. This is draft ITP and you need to modify it to meet your PO requirements.
|Transmitter Inspection and Test Plan Task||Vendor||TPI Inspection||Client|
|Temperature Transmitter mill test report||H||R||R|
|Temperature Transmitter Performance/Function test||H||W||R|
|Temperature Transmitter Visual / Dimension Inspection||H||W||R|
|Temperature Transmitter Insulation resistance test||H||W||R|
|Temperature Transmitter Documentation review prior to release(Final activity of Technical Inspection)||H||H||R|
|Temperature Transmitter Pre-shipment Inspection||H||H||R|
H: Hold Point implies that relevant production activities shall not proceed until the continuation of work is permitted by Purchaser. (Notification req’d)
W: Witness point implies that Purchaser intends to witness the designated inspection feature. If Purchaser decides not to witness the relevant feature, production can proceed without permission of Purchaser. (Notification req’d)
S: Witness, but spot check basis. Initial operation will be witness point and subsequent operation will be witnessed at discretion of Purchaser considering the results of previous inspection. (Notification not req’d : Randam Inspection)
R: Review inspection & test records (Notification not req’d)
General Note for Transmitter ITP:
1) Temperature Transmitter Witness/hold point by Code Inspector, when applied by Code /Local Regulation, is to comply with its requirements and to specify in Vendor’s ITP.
2) Type of Inspection by Temperature Transmitter Purchaser may be changed according to equipment criticality and vendor QC evaluation at job stage.
3) When requested in the requisition, detailed Temperature Transmitter ITP shall be submitted by Vendor.
4) Monitoring/Observation of Temperature Transmitter Vendor shop daily routine works (i.e. Storage of materials, Adherence to approved procedures, Testing tool calibration check, workmanship, cleanliness and etc.) shall be done by Purchaser during inspection visit.
5)100% Transmitter inspection which is covered by the combination of witness / spot check / record review inspection & tests listed above and vendor’s original
QC activity shall be confirmed by Purchaser’s inspector prior to shipment.
6)Unless otherwise specified in Temperature Transmitter REQ., the sampling Q’ty of ” S (Spot Witness Check) ” shall be as follows:
3 to 20→3Pcs(all if total 2 and less) , 21 to 50→5Pcs, 51 to 100→10Pcs,101 to 200→20Pcs, 201 to 300→30Pcs, 301 to 500→50Pcs
Minimum 25 pcs or more of the commodity shall be arranged for H/W/S inspection and test at one time inspector’s visit as much as practical.
7) Final Temperature Transmitter Visual Inspection/Documentation Review/Pre-Shipment Inspection may be combined within one time visit.
Temperature Transmitter installation :For the transmitter installation, the optimal method, known as direct mounting, is to have the transmitter integrally mounted with the sensor and thermowell. This installation method improves noise immunity through shorter sensor leads and their exposure to environmental electromagnetic interference (EMI). These transmitters can also be mounted remotely, but should be in close proximity to the sensor. For the mounting location, you’ll want to consider the ability to view the local operator interface display and any environmental issues such as vibration, corrosion, and ambient & process temperatures.
Temperature Transmitter Manufacturer
Temperature Transmitter Manufacturers / Vendors
ASHCROFT(DRESSER EUROPE GMBH)
CAMILLE BAUER AG
DELTA CONTROLS LTD.
ENDRESS & HAUSER
+44 1293 526000
FOXBORO ECKARDT GMBH
FUJI ELECTRIC CO LTD.
YOKOGAWA ELECTRIC CORP
|Yokogawa Electric Corporation|
Tech Reference :
Omega, Emerson , wika and inspection-for-industry.com