Epson manual Appendix I XDT Grounding Considerations, Sensor

XDT User’s Manual Appendices

Appendix I: XDT Grounding Considerations

Pluggable Block Terminals

Power Supply Module

4.3mH

0.5A 250V

1

AC LIVE

0.1uf

275VAC

Facility

2

AC NEUTRAL

0.0047uf

0.0047uf

3

Not Connected

AC Power

Earth

4

AC GROUND

Safety

RFI filter board

Ground

5

SIG-IN

p

white

o

o

Sensor

l

d

n

Measuring

6

SIG-RET

Sensor

u

o

r

Circuitry

black

g

e

s

7

A-OUT

Sensor casing connects to piping

u

a

0.1uf

1M Ohm

33V 400W

c

co

T

O

Analog Output 4/20mA

n

8

A-RET

cti

N

o

s

n

t

e

h

ro

ug

o

h s

d

.

9

TxD

tructur

tc

pese

al members pi

10

RxD

11

RET

Chart recorder,

12

PS+

A/D converter etc.

p

o

Possible Earth Ground at Analog Output monitoring equipment

o

13

l

AC GROUND

d

n

u

Logic ground and AC

o

14

Not Connected

r

Power ground are

a

g

connected for safety

e

and electromagnetic

15

NC

con

cau

s

interference

ne

cti

LD

on

thro

OU

considerations

LO

16

NO

RS 232 I/O

ugh e quipment grou

17

C

PC, Data Logger etc.

18

ALARMS

Not Connected

lo o

p

Possible Earth Ground at terminating equipment

d

19

NC

un

ro

g

a

20

NO

e

s

HI

u

con

a

c

21

C

nection thr ough equipment ground COULD

Instrument Circuit board

1.The sensor ground is isolated from the signal and frame grounds, however it is shunted to frame ground with a 33V Transient Voltage Suppressor,1M Ohm resistor and 0.1uF capacitor to prevent electrostatic buildup and noise pickup. When the sensor is connected to equipment which is grounded to earth ground (because of pipes etc.), there is no ground loop because the sensor is not connected to the earth ground on the circuit board.

2.The optional Analog Output and RS-232 Output are both referenced to the circuit board logic ground, which is jumpered at a single point to the AC power ground. Therefore if these out- puts are connected to equipment which connects the signal grounds to earth ground (this is a common occurrence in PC's), then a ground loop may be formed. This can be best avoided by removing the signal to earth ground connection at the termination equipment; if that is not possible then the AC power ground connection to XDT logic ground may be removed but this may cause a EMI problem. Please consult with your representative for information on optional isolated analog and RS-232 outputs. Keep in mind that in general, a ground loop on a digital line such as RS-232 will not cause problems.

3.The Earth Safety Ground (AC GROUND) at pin 4, should not be omitted since the RFI filter capacitors will cause half the line voltage to develop at the instrument’s ground. This may have safety and EMI implications.

4.When installing DC powered instruments (15 to 30VDC at pins #12 and #11), similar condi- tions may exist, if the DC power source is earth grounded.

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