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MODEL 1200 - USER MANUAL
The IQ model 1200 is a dual process trip
amplifier (sometimes called a dual alarmer)
which provides two adjustable relay outputs
from an analogue process signal (eg.
4~20mA). They offer an inexpensive method
of providing alarm and/or trip functions.
Changes have been made to the design over
the years, including the addition of extra
features, however new units may be used as
direct replacement for older units and are
totally pin compatible.
A model 1210 was produced for a short period
for special applications. This unit featured
programmable fail safe operation for 4-20mA
systems but the relay operation was limited to
de-energise on rise. The latest version of the
model 1200 now has this feature and the
model 1210 has been discontinued.
BASIC MODE OF OPERATION
Each relay output is associated with a set point knob on the front of the unit. The
set point knob may be calibrated directly in measured units (eg. 0-5volts) or,
more usually, as a percentage of the input signal (eg. 0-100% representing
4-20mA).
When the input signal exceeds either set point the related relay will change state.
When the input signal falls below the set point the relay will change back.
Whether the relay energises or de-energises on rise will depend on the setting of
DIP switches either on the front of the unit (newer models) or inside, accessed by
un-clipping the base (older models).
The hysteresis between relay energising and de-energising is typically 1.5% of
span.
Because the set point potentiometers are standard commercial types and the
scales on the knobs are small the absolute accuracy of the set point cannot be
guaranteed better than 5% of full scale. The repeat accuracy is however better
than 1% of full scale.
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POWER SUPPLY
The majority of units are supplied for 230V 50Hz or 110V 50/60Hz operation and
are fitted with miniature transformers. A 24V DC supply is generated internally
and this is made available on pin 6 to power 4-20mA loops or other equipment.
The maximum rating for this output is 30mA and later model units have a current
limiter set at around 25mA to prevent this from being exceeded. Some earlier
models were not current limited and it is possible to damage these units by
drawing excess current from this pin.
A small number of units have been supplied with 24V DC power supplies, usually
for voltage inputs. In the case of a 24V DC unit, pin 10 (power supply negative)
is internally connected to pin 7 (input negative). This is not usually a problem for
voltage inputs where the 0V rail is normally the common, however is not
recommended for current inputs (eg. 4-20mA) where +24V is usually the common
as it is almost certain to lead to ground loop problems.
Units supplied with a 24V DC power supply have pin 6 (+24V out) connected to
pin 2 (+24V supply), either directly or through a current limiter.
RELAY OUTPUTS
The model 1200 is fitted with two independent SPDT relays with a contact rating
of 10A at 250VAC. Voltages up to 400V AC may be switched provided the total
VA rating does not exceed 2500VA.
The manufacturer’s specification on the relays is 10
5
operations at full load and
10
7
operations at no load, so for maximum life we recommend using an external
relay or contactor if the current is greater than 5 amps.
SELECTING RELAY OPERATION
Because both relays have SPDT contacts many electricians assume that their
required function can be achieved merely by the choice of the NO or NC
contacts. This approach, although reasonable in a perfect world, makes no
allowance for the possibility of unit failure.
The best choice of operating conditions is that both relays should be energised
during normal operation and should de-energise in a fault condition. This ensures
that should the unit or one of its relays fail, or should the unit lose power, a fault
condition will be indicated. Usually fault conditions are on rising signals (eg.
Over-temperature, high vibration) however sometimes low levels can indicate
faults (eg. Under-temperature, low pH). For that reason the relays of the model
1200 are independently programmable.
