P7810A-D PRESSURETROL® CONTROLLER
7
65-0268—1
OPERATION
The P7810 uses integral electronic pressure sensors to sense
pressure at the inlet through an internal manifold. The control
sensor connects to the internal manifold with 1/4 inch NPT
threads and provides the pressure signal to control a relay for
the on/off control function. The same sensor provides the
information for the 4 to 20 mA firing rate modulation output.
A separate integral electronic pressure sensor is required to
provide the high limit function. This sensor also connects to
the internal manifold with 1/4 in. NPT threads. P7810C,D
devices contain two internal sensors and require a 1/2 inch
NPT mounting to the steam pressure header. Devices with
high limits lockout at setpoint and require manual reset when
pressure returns below the setpoint. Devices will not reset
with power interruption.
The P7810A is an on/off pressure control to start and stop a
burner system through a flame safeguard control. A 1/4 inch
NPT mounting is required to the steam pressure header.
The P7810B combines the on/off function of the P7810A with
providing a 4 to 20 mA modulation control output. A 1/4 inch
NPT mounting is required to the steam pressure header.
The P7810C has on/off function, 4 to 20 mA modulation
control output, and safety high limit function in one control. A
1/2 inch NPT mounting is required to the steam pressure
header.
The P7810D has on/off function and safety high limit function
in one control. A 1/2 inch NPT mounting is required to the
steam pressure header.
Pressure On/Off Control Function
(P7810A,B,C,D)
When pressure increases to the control setpoint, the control
relay contacts open. The relay contacts close when the
pressure decreases to a level at or below (differential) the
control range differential setting. This cycle continues until
power is removed, opening the relay. See Fig. 11.
Fig. 11. P7810 on/off control function versus pressure.
Modulate Control Function (P7810B,C Only)
When the pressure decreases to or below the modulation
setpoint, the current is 20 mA. The current remains constant
at all pressures below the modulation setpoint.
The modulation range is an additive value to the modulation
setpoint value.
When the pressure increases above the modulation setpoint,
the current decreases linearly until the modulation range point
is reached. The output current is 4 mA at and above this
pressure. See Fig. 12.
Fig. 12. P7810B,C modulation current versus pressure.
Limit Function (P7810C,D only)
The Limit potentiometer has two functions:
a. To set the
Maximum Fixed Stop Limit
. This is the
maximum pressure setting that the P7810C or D
control can be adjusted to and still perform its
intended function (i.e., safety shutdown).
CAUTION
Equipment Damage Hazard.
Exceeding pressure vessel limits can damage
equipment.
The
Maximum Fixed Stop Limit
pressure setting
must not
exceed the maximum working pressure
rating of the pressure vessel. Adjust the
Maximum
Fixed Stop Limit
setting to the maximum working
pressure rating that is stamped on the pressure vessel
by the manufacturer.
b. To set the
High Limit Setpoin
t. This is the desired
pressure value to which the P7810C or D control is
adjusted and at which it performs its intended
function (i.e., safety shutdown).
The High Limit Setpoint can be set lower than the internal
stored Maximum Fixed Stop Limit Value and will provide
system lockout at the knob setting. For example, the internal
stored Maximum Fixed Stop Limit Value is 12 psi and the knob
is set at 10 psi. System lockout is at 10 psi. The LED pattern
will be green on and yellow blinking slowly.
ON
OFF
CONTROL
RELAY
(K)
CONTROL
RANGE
PRESSURE
CONTROL
SETPOINT
M4881B
DIFFERENTIAL SETTING
20 mA
4 mA
MODULATION
CURRENT
MODULATION
SETPOINT
PRESSURE
MODULATION
RANGE
M4882
