OEM Explosion proof Differential Pressure Transmitter Price SPECIFICATIONS Huaheng Instrument is well-known as one of the professional and credible oem explosion proof differential pressure transmitter price manufacturers and suppliers in China for the high flexibility and good function of its...
Ambient Temperature Effects
Static Pressure Effects
Over pressure Effects
±0.1%×Span /3 years
Power Supply Effects
±0.001% /10V (12~42V DC)
Stainless steel 316L
Power systems use differntial pressure transmitters,
to measure liquid flow and liquid levels,
and people have become accustomed to their traditional installation methods.
In recent years,
Huaheng found in the process of maintenance and repair of thermal engineering,
that there are many misunderstandings in the traditional installation method,
which is necessary for improvement.
Most of the on-site liquid flow,
and liquid level measurement adopts the differential pressure measurement method.
In operation, the flow rate is not accurate or the liquid level deviation is large.
The usual treatment method for thermal maintenance personnel,
is to check the transmitter or disassemble the transmitter. Check back, and pay little attention to the installation of the live meter.
Second, the traditional installation method for the requirements of the pressure pipe.
Measuring the flow or level with a differntial pressure transmitter.
The traditional installation method for the pressure tube is as follows:
1) The pressure guiding tube will be made of pressure-resistant and corrosion-resistant materials,
according to the nature and parameters of the fluid (or liquid level) to be tested. The inner diameter must not be less than 6 mm and the length must be within 16 m.
2) The horizontal laying of the pressure guiding pipe should be inclined.
When the horizontal laying length of the pressure guiding pipe exceeds 30m,
it should be inclined in sections.
3) To avoid the transmission of static differential pressure signal,
the positive and negative pressure piping should be as close as possible.
The pressure piping of the easy-to-condense and easy-to-freeze medium，
should be insulated with electric heat, steam or hot water.
The differential pressure flow transmitter uses a pressure guiding tube，
to send the static differential pressure,
generated upstream and downstream of the throttling element,
to the measuring chamber of the differntial pressure transmitter,
and then converts the static pressure difference into a standard signal (usually 4 to 20 mA).
The differential pressure transmitter,
is generally installed in the local instrument cabinet
(insulation box) on the ground or platform,
and then the special heat preservation and heat tracing pipeline is laid.
Third, the traditional long lead pipe installation method defects
1) The pressure piping is too long, wasting installation materials. Taking the differential pressure flow measurement system as an example,
the normal installation requires at least 2 positive and negative pressure cut-off valves,
2 packages, 2 positive and negative secondary valves,
1 balance valve, 4 blowdown valves, and a union.
the pressure pipe length is about 10 ~ 30m, the elbow is 6 ~ 7,
the heat pipe is 20 ~ 40m, if the hot water is used, it needs 2 hot hand valves, 1 steam trap,
1 heat preservation cabinet, insulation cotton, insulation cloth.
2) There are many accessories for the pressure piping,
the leakage points increase, and the maintenance workload increases.
3) Delay the transmission of differential pressure signals.
The longer the pressure transmission line, the more the elbows,
the slower the transmission speed of the differential pressure signal.
4) The heat consumption of the heat is large.
If a differential pressure flow transmitter uses hot water heating,
the temperature drop before and after the heating is 20 ° C (90 ° C down to 70 ° C),
the initial estimate of the hourly heating requires about 100 kg of hot water,
then a power plant How many such transmitters must antifreeze and heat tracing,
and their heat consumption is considerable.
5) Generate more measurement errors.
For example, a differential pressure flow transmitter,
with a spacer solution has a range of 0 to 40 kPa for a primary meter,
a range of 0 to 40 t/h for a secondary meter, and a media density P/media = 0885 g/mm3.
The density of the glycerol in the isolation liquid is p=g/mm3,
and the vertical height of the orifice plate to the flow transmitter is =1mm.
If the isolation liquid in the negative pressure tube is completely leaked,
the negative pressure tube will be filled with the medium.
As a result, the measurement glycerin in the positive pressure tube,
and the negative pressure in the negative pressure tube cause additional measurement errors.
This error can be obtained by the following calculation:
The additional flow error is: qm2=qm2max(Δp/ΔPmax)1/2=40×(5.626/40)1/2=15t/h
This absolute error of 15t/h is the error when there is no flow in the pipeline.
The leakage flow in the negative pressure-inducing tube,
is leaked after the negative pressure-carrying tube is filled with the medium.
If the flowmeter shows 40 t/h flow, what is the actual flow rate? What is the flow error? It can be obtained by the following calculation.
When the flowmeter shows a flow rate of 40t/h, the differential pressure of the throttling element is:
The corresponding flow rate is: qm2=qm2max(△P∥△Pmax)1/2=40×(34.375/40)1/2=37t/h
Then add: 40-37 = 3t / h flow.
So, once the isolation liquid in the negative pressure pipe leaks,
the additional measurement error caused by it is between 3 and 15 t/h.
Fourth, the advantages of improvement
The principle of measuring the flow rate,
by the differential pressure transmitter shows that,
the length of the impulse tube is not related
to the magnitude of the differential pressure signal transmitted,
when the flow rate is measured by the differential pressure transmitter,
and the pressure tube only serves to transmit the static pressure.
The pressure guiding tube can be long or short.
Under the conditions of the installation environment,
the pressure guiding tube can be shortened as much as possible,
part of the mounting accessories can be cancelled,
part of the installation materials can be saved,
and the transmission speed of the differential pressure signal can be accelerated.
The temperature of the fluid transport medium in the pipeline is high,
so the energy radiated by the fluid transport pipeline itself,
forms a high temperature zone around the pipeline.
In the installation of differential pressure transmitters that require anti-condensation and anti-freezing media,
the measuring chamber of the differential pressure transmitter,
can be brought close to the conveying pipe,
while the pressure-inducing pipe is shortened,
and the radiant heat of the pipe is used as the instrument heating, so as to save heat.
Water, hot steam or electrical energy, ie direct installation of white heat.
The improved differential pressure transmitter has the following advantages,
because the measuring chamber is close to the fluid conduit and the impulse tube is short:
1) After the shortening of the pressure guiding tube,
the measuring principle and measurement accuracy are not affected,
and a large amount of installation materials are saved.
An improved differential pressure transmitter pressure tube,
takes about 1 to 2 m long,
which is much less than the traditional installation method.
2) The pressure guiding tube is short, and the pressure piping has few attachments.
The pressure from the pressure tapping hole to the meter head,
generally does not exceed 1-2 meters,
the leakage point is reduced, and the maintenance workload is reduced.
3) The differential pressure transmitter,
that needs to be anti-freeze can use the radiant heat of the pipeline,
to heat the instrument,
and does not need to lay special electric energy, steam or hot water heating pipeline.
Save heat on heating installation materials and heat tracing energy to reduce costs.
4) Speed up the transmission of differential pressure signals.
5) With reference to the installation improvement method of the differential pressure transmitter,
the installation of some pressure transmitters can also be improved in this way,
which can reduce the workload such as waterway correction.
Five, pay attention to the following matters
In the above improvement process,
the following two points should be noted to avoid difficulties,
in future maintenance and measurement stability.
1) Since the pressure guiding pipeline is shortened,
the measuring head is very close to the throttling element,
so the installation of the throttling element,
and the measuring head should be as close as possible,
to the ground or the working platform,
so as to facilitate future routine maintenance, calibration adjustment and disassembly maintenance.
Work is going on.
2) Differential pressure transmitters,
that need to be accompanied by heat,
such as the measurement chamber,
of the differential pressure transmitter is enclosed in the insulation layer,
and the distance between the measurement chamber,
and the pipeline of the transmitter is based on the temperature,
of the fluid in the pipeline and the temperature generated by the radiation of the pipeline.
It depends on the height,
but it should meet the temperature requirements,
of the working environment of the transmitter.