Transmitter Circuit - Emerson Fisher 4200 Instruction Manual

Instruction Manual
D200354X012
Figure 9. Transmitter Operation
TRANSMITTER
MECHANICAL
CONNECTION
TO DEVICE
NOTES:
1 THIS EQUIVALENT CIRCUIT IS TYPICAL FOR ALL TYPES OF TRANSMITTERS. GENERALLY, IF A PORTION OF THE
CIRCUIT IS NOT USED, IT IS OMITTED.
RECEIVING DEVICE MAY BE ANALOG CURRENT INPUT TO DISTRIBUTED CONTROL SYSTEM, PROGRAMMABLE
2
LOGIC CONTROLLER OR INDICATING DEVICE. INDICATING DEVICE CAN BE A VOLTMETER ACROSS 250 OHM
RESISTOR OR A CURRENT METER.
3 FIELD WIRING FOR POSITION SWITCHING CIRCUITS CAN BE A TWO OR THREE WIRE SYSTEM DEPENDING ON
THE APPLICATION REQUIREMENTS.
4
SEPARATE RETURN REQUIRED FOR RELAYS. RETURN WIRE MUST BE CONNECTED EVEN IF RELAY OUTPUTS ARE
NOT USED.
B1946‐4/IL
The position switch circuit is driven by the same input system as the transmitter (except for the 4215 transmitter). The
position switch circuit acts as an electronic switch that controls two relays. The voltage present at the wiper of the
potentiometer is compared to the settings of the high and low position switch set points and provides an on or off
condition for the relays. Instruments that use a single element potentiometer use the same element for both the
transmitter input and the input to the position switch circuits. A 4215 transmitter with dual element potentiometers
uses one element of the potentiometer for the transmitter input and the other element for the position switch circuit
input. On an instrument with position switches only, the single element potentiometer is used for the position switch
circuit input. Each of the position switch circuit outputs is connected to a relay on the field circuit printed wiring board,
and depending on the potentiometer position, the relays are energized or de‐energized.

Transmitter Circuit

At all times, the current flow into the transmitter equals the current flow out of the transmitter. The current flowing
into the transmitter divides between a regulator circuit and transistor Q1.The regulator circuit establishes two
voltages one of which is (VREF). This voltage is applied across the input potentiometer. The other voltage, (VREG)
powers the Op Amps.
On units with position switches, the transmitter voltage regulator, 4 to 20 mA signal, and relay coil currents flow in the
wire between the power supply (+) terminal and the (+) terminal on TB3. The transmitter voltage regulator, switching,
and relay coil currents are returned to the power supply common from the (R) terminal on TB3. The 4 to 20 mA output
TRANSMITTER
PRINTED WIRING
BOARD
TRANSMITTER
CIRCUIT
SWITCHING
CIRCUIT
FIELD CIRCUIT PRINTED
WIRING BOARD
K1
RELAY
K2
RELAY
4200 Transmitters
24 VOLT
+
DC POWER
SUPPLY
-
4
DEVICE
+
RECEIVING
4 TO 20 MA
DC SIGNAL
-
2
DEVICE
RECEIVING
HI POSITION
SWITCH OUTPUT
(CONTACT
CLOSURE)
DEVICE
RECEIVING LO
POSITION SWITCH
OUTPUT (CONTACT
CLOSURE)
March 2011
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