The Model 340 Trip Amp is
SIL 2 Compliant according
to IEC 61508. Rated for –30C to
+75C,
it can be installed in the process unit near the equipment under control, even under
the harshest conditions, thereby
reducing implementation costs.
The Model
340 Trip Amp receives an analog or digital
process signal. Two field-adjustable setpoints allow
shutdown to be executed for high and low process signals.
Serial or hardwired communications are used to remotely
display process variables and system alarms.
With its 5 Amp output rating, the Model
340 Trip Amp can de-energize multiple final
elements, including motor control circuits and/or
solenoid operated valves.
Each Model 340 Trip Amp consists of
the following elements:
- Power supply
- Current loop receiver (I/U converter,
differential or single ended input)
- Low comparator
- High comparator
- Trip delay timer
- Turn-on delay timer
- Trip relay
Power Supply
The power supply uses the +24V field
supply to generate the ±15V voltages needed
by the Trip Amp. A polarization protection diode and
an over-current fuse protect the supply input.
Current loop Receiver
The high precision, low compliance voltage
current loop receiver converts a differential or single
ended sensor current input (4-20 mA) into an equivalent
voltage level. It also provides an external voltage
reference for the comparators so that any shift in
reference voltage will be ratiometric and will not
influence the trip thresholds.
Characteristics
Characteristics |
Nominal |
1)
Input impedance in signal range (in the ON or
OFF state) |
75
ohms |
2)
Analog input error: |
|
Maximum
error at 25 °C |
±
0.01% of span (16 mA) |
Temperature
coefficient |
±
0.02% of span/ deg C |
3)
Maximum error over full temperature range |
±
% of full scale/K |
4)
Maximum permanent allowed overload (no damage) |
40
mA |
5)
Output reading under overload condition |
high
trip condition |
6)
Type of input |
4-20
mA |
7)
Common mode characteristics (DC, AC 50 Hz, AC
60 Hz) |
differential |
8)
Operating modes |
Continuous
conversion |
9)
Type of protection |
R –
current limiter |
10)
Isolation potentials under normal service conditions
between channel and
a) other circuits(including ground),
b) between channels,
c) power supply(ies) and
d) interface(s) |
240
VAC |
11)
External power supply |
24
VDC +/- 10% |
12)
Common points between channel if any |
none |
13)
Type, length of cable, installation rules recommended
to provide interference immunity |
Shielded
twisted pair |
14)
Calibration or verification to maintain rated
accuracy |
Proof
test |
15)
Terminal arrangements |
24
to 12 AWG |
16)
Typical example(s) of external connections |
Valve
solenoids / Motor starters |
17)
Effect of incorrect input terminal connection |
Inputs
are polarity protected |
Low Comparator
The low comparator compares the I/U
converted sensor signal with a preset trip threshold.
The threshold voltage is adjusted via a high precision
10-turn potentiometer. If the sensor signal falls
under the threshold, the comparator changes output
and the trip delay circuit is triggered. The low comparator
and high comparator outputs are diode wired-OR combined
at the input to the delay circuit.
High Comparator
The high comparator compares the I/U
converted sensor signal with a preset trip threshold.
The threshold voltage is adjusted via a high precision
10-turn potentiometer. If the sensor signal raises
above the threshold, the comparator changes output
and the trip delay circuit is triggered. The wired-OR
connection of low and high trip signals ensures that
either trip is propagated into the delay circuit since
both trip signals have identical polarity.
Trip Delay Circuit
The trip delay circuit delays the actuation
of the output relay by an adjustable time (0.2 – 3
seconds). The delay time is adjusted via a high precision
10-turn potentiometer.
Turn on Delay
The turn on delay prevents relay flutter
when the supply voltage to the channel electronics
is applied. It holds the relay transistor in the OFF state
until the internal 15V supplies have stabilized. The
Turn on Delay does not influence the trip delay time.
Trip Relay
If the sensor signal exceeds the low
or high threshold longer than the trip delay time,
the trip relay is activated. If the senor signal returns
into the normal range before the delay time is expired,
the trip is not asserted.
Characteristics
(per connector) |
Nominal |
1)
Maximum output current (resistive) |
5
A |
2)
Maximum switched voltage (resistive) |
120
V |
