Answer / carl_ellis

You are looking at the RS-485-side of an RS-232/RS-485
converter and the power supply voltage for the converter is
+5V. Under idle conditions (no transmission), and assuming
you have enabled the RS-485 output: what would you expect
at: (a) Output A measured against output B (b) Output A
measured against ground (c) Output B measured against ground

With a supply voltage of 5V, the sink driver is usually able
to pull the voltage on each conductor fairly close to signal
ground (0.5V), but the source driver usually has a voltage
drop of approximately 1-1.5V. The voltage swing on each
conductor is therefore typical 3-3.5V, but it may be as low
as approximately 2V.

Answer a)
Hence, output A (-) measured with respect to output B (+)
would read approx -3V to -3.5V ( a negative voltage) in the
idle state. (The logic is inverted: a negative voltage is a
mark or logic 1)

Answers b and c)
Output A (-) measured with respect to ground: ~3.5V to 4V
Output B (+) measured with respect to ground: ~0.5V to 1V

This is a 3V differential, with 2.5V Vcm common mode, where
common mode is the mean of the differential plus the Vcm
common mode above the reference ground.

Carl Ellis
Measure First

Why 4mA-20mA current loop selected as standard ???

1 Answers   IMCO, Reliance,

---

Please any one can explain how to calibrate transmitter (smart) online with out remove from the container suppose it is interface level or static pressure level measurement we dont want to remove transmitter from the container mean it is running plant please give me detail. thankx brothers

1 Answers   KNPC,

---

in current transmitter why we use 4-20ma ???

2 Answers   IMCO, IOCL,

---

hi,i am doing 3 year in electronic and instrumentation engineering. what type of aptitude questions will be asked in a core industries and how can i improve my skills in instrumentation?

0 Answers  

---

My rtd working well at the same time r/i converter is not working properly.when power is given to rtd..it is giving 30mA and getting 2.4 mA if i remove the compensate leads No matter how many ohms.why it is happening like so?what is the solution?rtd range-0-200deg c& 4-20 mA o/p.please give me solutiin anyone......

1 Answers  

---

i have a dp tx range is 5000mmwc. in which calibration i use in a open tank.1.5*3.5*2.5 mtr.for level msmnt. what is the calculation.

2 Answers   Bajaj Hindusthan,

---

whether radar level transmitter is applicable for the open tank

1 Answers   TCL,

---

suggest a sensor to measure rapidly varying temperature?

1 Answers  

---

Anybody know how to create a ladder programme for power switch in TV remote without using counter... ie TV can be turn on and turn off using single push button switch... on pressing the switch first time TV turn on and hold the on state till i press the switch again, and after TV turn off.

2 Answers  

---

Explain Three way boiler.

2 Answers   L&T,

---

what is axial shift n what is differential expansion in turbine? how many sensor probes r mounted for this n how it works?

2 Answers   Apple,

---

what is relation between electronics&instrumentation

4 Answers   Hindustan Zinc,

---