Answer / carl_ellis

Atmospherice pressure equals zero pressure (gauge).

Vacuum pressures are less than atmospheric so are negative with respect
to atmospheric pressure. -100mm would be a vacuum pressure.

Pressures above atmospheric are positive with respect to atmospheric
pressure.

Carl Ellis
Measure First

Answer / carl_ellis

-100mm wc is a vacuum with respect to atmospheric pressure
as a reference.

Given the range, the pressure transmitter is likely a
differential pressure transmitter.

-100mm wc pressure can be produced with a vacuum source,
like a hand pump connected to the high side, with the low
side open to atmosphere.

Or 100mm wc positive pressure can be applied to the low
side, with the high side open to atmosphere:
DP = high side minus low side
DP = 0 minus 100 = -100mm wc

The URV, 300mm wc, is a calibrated with a pressure source
connected to the high side, with the low side open to the
atmosphere.

Carl Ellis
Measure First

Why we are using reverse action in displacer types level transmitters on some Vessels?

0 Answers  

---

we want to control pump in let pressure and tank (for exp) our inlet line if water cam and pump will on and when our tank will full pump will off also if our inlet pressure low pump will off even tank not full.this pump i want to uses on our water supply line.

0 Answers  

---

what is absolute pressure, gauge pressure and atmospheric pressure?

2 Answers   Mother Dairy,

---

as an instrumentation engineer which are the things we have to know / or we must have idea about that....

2 Answers  

---

We are using Rosemount 5400 series Radar Level Transmitters in all types of Sump Applications having oily water hdrocarbon petrochemical nature. What we are facing the problem frequently is that always getting reading frezzed at some value. If we do power recycling , sometimes it is working . then making same freezing problem. If anybody faced before such type of problem and also having solution , Please give the answer.

0 Answers   Sabic,

---

you are on site,the plant trips,you are approached by operations,what do you do?

0 Answers   ABB,

---

a pressure transmitter with a range of 0 to 2500kpag has a specified accuracy of 0.5 % of span.It is to be calibrated using a comparison gauge to have an accuracy of 0.1% of span.The comparison gauge has a range of 0 to 3000kpag What is the accuracy ratio? is this ratio acceptable?

1 Answers  

---

what is the procedure to callibrate temp controller ,pressure controller,etc. suppose a temp controller showing error 1.5 degree centigrate how can i minimize it.

0 Answers   Sabic, Saudi Aramco Shell Refinery Company SASREF,

---

What s the exact height of installed transmitter?

1 Answers  

---

What is the function of SMPS

2 Answers  

---

when the operation engineer told you that he gives the control valve order to open but there is no response ! what will you do ? and if you found that there is astuck , what will you do ? (note : it is apanumatic valve )

5 Answers  

---

How to calibrate DP transmitter by using HART communicator ?

1 Answers  

---