Applications Guide
Modline 5
131
Zero current output (0 or 4 mA), as selected, equals the corresponding zero scale temperature. A 20 mA
reading corresponds to the full scale temperature. Since the output current varies linearly with
temperature, equal increments in current will provide equal increments in temperature between these
range limits.
Expressed as a formula for the 4-20 mA analog output is:
T
IND
= ( ( (
I
– 4)
16) X (T
F.S.
– T
Z.S
.)) + T
Z.S.
Expressed as a formula for the 0 -20 mA analog output is:
T
IND
= ( (
I
20) X (T
F.S.
– T
Z.S
.) ) + T
Z.S.
Where
I
is the current loop output in milliamps
,
T
F.S.
is the corresponding full scale temperature and T
Z.S.
is the Zero Scale Temperature,
Example: For a 4-20 mA analog output, with a 16 mA span, corresponding to the 500 to 2500 degree range
and an output current of 8 mA:
T
IND
= ( ( (
8
– 4)
16 ) X (2500 – 500) ) + 500 = 1000 degrees
Example: For a 0-20 mA analog output, with a 20 mA span, corresponding to the 800 to 1800 degree range
and an output current of 8 ma:
T
IND
= ( (
8
20 ) X (1800 – 800) ) + 800 = 1200 degrees
8.2.3
Analog Output Operation Notes
1.
The Analog Signal Output is affected by the selected Response Time Value and by any Peak
Picker or Track and Hold signal conditioning selections.
2.
Three Analog Output related alarm functions can be used to set the Analog Current Output to a
specified value for certain conditions. A–LO, A–HI and FATL alarm functions will force the
current output to specific values for Zero Scale, Full Scale and two alarm conditions (Sensor
failure and Dirty Window Detector operation Failure). See Section 5
, page 82 of this
manual for setup instructions.
3.
A 10 Volt d.c. full scale signal can be developed by shunting the analog current output with a
precision 500 ohm resistor. See Section 4
, page 64 of this manual for more
information.
8.3
Response Time
8.3.1
Description
Response Time is the length of time it takes for the displayed temperature, the analog current output
signal, and digital output to reach approximately 95% of a step change in measured temperature.
The Response Time in the Modline 5 Sensor has an adjustable range from 6.6 or 10 milliseconds
minimum, depending on Model, to 60 seconds Maximum. See section 2
this manual for Response Time restrictions by Model. The Response time can be set using the HEAD
menu RT function and RS-485 Digital Communications.
If you find that process temperature variations or signal noise is interfering with your measurement or
control system, increase the Response Time as required.
