Automated Water & Effluent Ltd



AWE Ltd Watermark

AWE Ltd Winter Watermark 2013

TAP Series of Piston Plunger Dosing Pump

To compliment our range of TAM Mechanical Diaphragm Motor Driven Dosing Pumps as featured in the Autumn 2012 issue of the Watermark we have an even larger range of piston dosing pumps offering greater flow rates and pressure outputs.

The TAP series of piston dosing pumps is based on the same gearbox with a modified cam arrangement. With two stroke lengths 15 and 25 mm. combined with a wide selection of piston diameters and 3 stroking speeds we are able to offer outputs from 0 - 1.5 Litres / Hour up to 1000 Litres / Hour. The length of the stroke may be manually adjusted by a micrometer dial adjustment from zero to 100%. For automatic control a servo motor controlled by an industry standard 4 - 20 mA current signal can be specified and fitted during manufacture. Pump head materials are either stainless steel with a stainless steel piston or PVC with ceramic piston. Electric motors are usually 400V 3 Phase with an option for 230 VAC single phase and Ex-D if required. For use with inverters we are able to fit oversized motors or for applications which may require long periods of slow running or installation in hot areas we are able to offer fan assisted motors for improved cooling.

Multifunction Valves

Having included in our Autumn 2012 technical tips an article on the AC-VM multifunction valve we are pleased to announce an improved version of the multi function valve to be supplied during the first quarter of 2013. Improvements for the new MF Valve are the complete valve is moulded in PVDF for greater chemical resistance. The back pressure or loading valve function is adjustable up to 5.0 bar and the pressure relief or safety valve function is adjustable up to 18.0 bar. The new part number is AC-VM-PVDF and it can be supplied with Viton or EPDM seals and with either fittings for 4 x 6mm or 8 x 12mm hose sizes. Please contact the sales office for the full part number.

Temperature Measurement

After 30 years in business we at AWE are well known for our Effluent and Water treatment instrumentation dosing and controls. However as instrumentation engineers we also supply other types of instrumentation the biggest measured and controlled parameter of all is temperature. With applications ranging from space heating to the control of steel making and heat treating processes. Temperature sensors range from simple bi metal strips to optical pyrometers for non-invasive measurement.
The vast majority of traditional industries temperature measurement and control relies on either thermocouples or resistant thermometers as the two are totally different to follow is a brief description of both sensors as they can look the same are so are often assumed to be the same.

Thermocouples

Thermocouples are two wire devices made up from dissimilar metal welded together which when heated produce a small millivolt potential. The output depends upon the materials of construction with a whole range of different materials for differing applications and temperature ranges, which is way beyond the scope of this article. For example a general low cost thermocouple would be a type K which is manufactured from Nickel and Chromium and produces an output of 41μV/oC being a magnetic material can cause some problems with linearity at temperatures above 350ºC this is again outside the scope of this article. For higher temperature applications Type B, R or S can be used up to 1600ºC these thermocouples are considerably more expensive being manufactured from Platinum / Rhodium with an output of 10μVºC.

The disadvantage of thermocouples is they cannot be connected to standard copper cable as another junction of dissimilar metals would be made in the connecting head which would also produce a millivolt signal and hence an error. So a cable with the same characteristics as the thermocouple must be used to connect back to the temperature controller this is called compensating cable. The connection at the instrument terminals with the comp cable can produce a small millivolt potential which needs to be compensated for this is often referred to as the cold junction temperature.

Thermocouple Styles

TPA-1-N

thermocouple style TPA1-N

TPA-1-A Thermocouple Temperature Probes. The assembly is with a die cast alloy connecting head.

The TPA1-N Thermocouple Temperature probe has a 1/2" BSP mounting thread to screw into either a process connection or pocket.


TPA-2-A

thermocouple style TPA1-N

The TPA2-A Thermocouple Temperature Probes. The assembly is with a die cast alloy connecting head. With a straight plain 6mm diameter stem. (Stem size length or diameter is available be specified on order). It is not recommended that the TPA2-A thermocouple is installed through a compression fitting or mounted horizontally due to the weight of the head.


Thermowell or Temperature Pocket TPP1

Temperature Pocket TPP1

Temperature Probe Pocket or Thermowell TPP1 for use when the probe cannot be removed from the process for calibration or maintenance without stopping the process.


PRT Theory

The temperature instrument or transmitter supplies a low voltage to the platinum resistance sensor which causes a current to flow; making an electrical circuit.

By ohms law the voltage drop in the circuit and hence the current flow is proportional to the resistance in the circuit. As the temperature increases the resistance of the PT100 increases:- this is a positive temperature coefficient. The problem with the two wire configuration is the instrument reads the resistance of the connecting cable as well as the temperature sensor.

There are some simple ways to circumnavigate this problem has listed below in the connection details for the 3 & 4 wire systems.

Connections for two wire instruments

Temperature connections for 2 wire instrument

Red Wire

White Wire

In this circuit the resistance is 3 + 100 + 3 Ω = 106 Ω


Connections for three wire instruments

Temperature connections for 3 wire instrument

Red Wire

Red Wire

White Wire

In this circuit the temperature instrument measures the resistance between the red and white wires, it also measures the resistance between the two red wires.

The temperature controller will subtract the resistance between the red wires from the resistance between the red and white wires to compensate for the resistance in the cable. The instrument assumes that the resistance in all the wires are equal to each other.


Connections for four wire instruments

Temperature connections for 4 wire instrument

Red Wire

Red Wire

White Wire

White Wire

The four wire connections are usually connected to the four arms of a wheatstone bridge type circuit so that the resistances cancel each other out.

In our opinion the cost of installation of a long cable run is greater than installing a 4-20mA two wire temperature transmitter.

A two wire 4-20mA temperature transmitter offers precision signal transfer over an effective distance up to 1000 metres away. We would suggest the TT100 4-20mA Temperature Transmitter paired with a BC7635 Controller as a suitable alternative.

 

Platinum Resistance Thermometer Table

Temperature

Resistance

-100ºC

60.26Ω

-50ºC

80.31Ω

-20ºC

92.16Ω

0ºC

100.00Ω

20ºC

107.29Ω

25ºC

109.73Ω

30ºC

107.67Ω

50ºC

119.40Ω

75ºC

128.98Ω

100ºC

138.51Ω

150ºC

157.33Ω

200ºC

175.86Ω

 


Temperature Sensor Dimensions

TPA-1 Series

The TPA-1 Series of temperature sensor have a 75mm long by 12.5m diameter lagging extension.

 

TPA-1-N

TPA-1-N Temperature Sensor Dimensions

TPA-1-N Temperature probe assembly in 316 Stainless Steel with ABS connecting head with terminals or optional two wire transmitter.

 

TPA-1-A

TPA-1-A Temperature Sensor Dimensions

TPA-1-A is as per the TPA-1-N, with a die cast alloy connecting head usually fitted to thermocouples.

TPA-2 Series

The TPA-2 series of temperature sensor have a 316 stainless steel shaft parallel for the whole length.

TPA-2-N

TPA-2-N Temperature Sensor Dimensions

The TPA-2-N in 316 Stainless steel with ABS connecting head with terminals.

 

TPA-2-N-PTFE

TPA-2-N-PTFE Temperature Sensor DimensionsThe TPA-2-N-PTFE temperature sensor has a 316 stainless steel shaft parallel for the whole length and sheathed in PTFE with a PVDF bush. This means that no metal parts are exposed.

 

TPA-3

TPA-3 Temperature Sensor Dimensions

The TPA-3 Temperature probe assembly in 316 stainless steel with a Hirschmann removable connector.

The TPA-3 is available with an option stainless steel compression fitting with 3/4" BSP male thread or other as specified.

Resistant Thermometers (RTDs)

Our resistant devices are usually made from platinum which have an extremely accurate and linear resistance change with temperature. The PT100 being 100Ω at 0ºC and 138.51Ω at 100ºC. An RTD can be used for higher temperatures up to 650ºC. In theory they become quite fragile at temperatures above 300ºC. As our RTDs are mainly used for liquid and ambient air temperature measurements this has never been a problem. The disadvantage with RTD Sensors is that the cable from the sensor to the controller can add resistance to that of the sensor creating errors. So many instruments incorporate circuits for 3 or 4 wire sensors where the addition conductors are connected to a bridge circuit to compensate for the cable resistance.

As a rough rule if the cable conductors are all the same resistance a 3-wire input works well on long cable runs.

Where there could be some difference in the resistance of the conductor a 4-wire input would prove better.

Overall a better solution to the problem of long cable runs is to fit a two wire transmitter into the sensor head where the RTD sensor resistance is converted into an industry standard 4-20mA signal which can be run up to 1000m using our LMK2 connecting cable.

We offer 3 standard styles of temperature sensor as follows and can manufacture others to order.

TPA-1

TPA-1 Temperature Sensor

TPA-1 Stainless steel insertion temperature sensor with 6mm diameter and insertion length as specified.

The TPA-1 has a 1/2" BSP male thread and 75mm long lagging extension fitted with either ABS or Alloy connecting head.

The TPA-1 can be used with either a 3 wire RTD or a thermocouple type TBA.

The 1/2" BSP mounting thread can be screwed into either a process connection or a temperature pocket.

TPA-2

TPA-2 Temperature Sensor

TPA-2 Stainless steel insertion temperature sensor with 6mm diameter and insertion length as specified.

The TPA-2 insertion temperature sensor can be supplied with compression fitting usually fitted vertically into process tanks.

For longer immersion lengths the riser tube can be manufactured 12mm in diameter or greater as required.

TPA2-A-PTFE

TPA-2-A-PTFE Temperature Sensor with PTFE sheath

 

This version of the TPA-2 Temperature probe assembly has an ABS connecting head and PTFE sheath.

This is suitable for aggressive chemicals where stainless steel cannot be used.

The straight plain 6mm diameter or larger diameter stem is ideal for immersion into a process.

The option for a PTFE sheath is ideal for solutions where stainless steel is unsuitable. Use code TPA-2-A-PTFE for the PTFE sheathed Temperature Probe.

TPA-3

TPA-3 Temperature Sensor sheath

TPA-3 Stainless Steel insertion sensor is 6mm diameter and fitted with Hirschmann connector for easy removal and refitting.

This is suitable for PRTs only.

The Hirschmann connector allows easy replacement of the sensor. The straight plain 6mm diameter stem is ideal for immersion into a process or insertion into a TPP2 Temperature Pocket.

TPP2 - Temperature Pocket

Temperature Insertion Pocket with BSP fiting

The TPP2 is a Temperature Probe Pocket for use where the probe cannot be removed from the process for calibration or maintenance without stopping the process.

4-20mA Temperature Transmitter TT100

2 Wire Temperature Transmitter 4-20mA current output

The TT100 is a Two Wire Temperature Transmitter for mounting inside one of our temperature probe heads.

The TT100 temperature transmitter converts the 3 wire RTD Sensor into a 4-20mA current signal.

The TT100 is powered by the receiving instrument and we recommend pairing the TT100 with our BC7335 or BC7635 control instruments for simple installation, loop power, and the give relay control based on the temperature into your process.

 



Dosing Pumps Exhibited At Surface World

If you need data sheets or hand books on the TAP series of Piston Plunger Pumps or the TAM Series of Mechanical Diapragm Dosing Pumps then please contact us by telephone on 01785 254 597

AWE-Ltd 2013 Catalogue

The Automated Water & Effluent Ltd 2013 Catalogue is now available. If you would like to request a copy please call the sales office on 01785 254 597.

Multi-function Valve model AC-VM in PVDF

The AC-VM Multifunction valve producted in PVDF for greater chemical resistance. The AC-VM is available with either Viton or EPDM for use in your process.

Contact AWE Ltd sales on 01785 254 597 for more information or to purchase our products.