Honeywell VRX180 Time Proportioning Relay Driven Pump, Function Block Diagram Of Figure

Programming and Operating Concepts

Time Proportioning Relay Driven Pump

A second control scheme is to use a relay to produce a time proportioning or Duration Adjusting Type (DAT) control signal. Such an application is depicted in Figure 3-17.

INSTRUMENT

PV 4.00

SP 7.00

OUT 90.5%

	LINEAR pH
	TRANSMITTER
4 TO 20 mA	4.00
	pH

DAT CONTROL

SIGNAL

CAUSTIC

REAGENT

PUMP

WASTE WATER TREATMENT VESSEL

WITH IMMERSION STYLE pH ELECTRODE

AND MIXING IMPELLER

Figure 3-17 Control Of Wastewater pH Using A Time Proportioning (DAT) Control

Signal

This application requires a basic time proportioning control loop to monitor and control the pH of the wastewater to a local set point of 7 pH units. That is, the loop will “neutralize” the wastewater so that it can be safely released to the environment. The wastewater pH, which is assumed to be primarily acidic, will be controlled by introducing a caustic reagent to the contents of the treatment vessel. This will be done through use of a time proportioning relay signal that will pulse a pump connected to a caustic reagent source.

A function block diagram representing the control scheme of Figure 3-17 has been drawn in Figure 3-18. The same diagram method was used to produce Figure 3-16.

AO1 BC

250Ω

4 TO 20	+	AI1 OV		FB			CONNECT
	1 TO 5
			PV				TO PUMP
mA	VDC	AI1			LP1 OV
							%
	-			LP1	IN AO1	DO1

RANGE LOW = 0
RANGE HIGH = 14	TYPE = STANDARD
CIRCUIT LOW = 1
CIRCUIT HIGH = 5	SP1 = 7.00

OUTPUT TYPE = DAT IN LOW LIMIT = 0

IN HIGH LIMIT = 100 IMPULSE TIME = 150

Figure 3-18 Function Block Diagram Of Figure 3-17

This drawing is similar to the temperature control application. The analog input, control loop, and analog output function blocks (AI1, LP1, and AO1) have been used similarly. The discrete output function block was added, drawn as a circle at AO1’s apex and named “DO1.” Recall that any analog input, control loop, analog output, or discrete output available may be used. Up to 36 discrete outputs (DO1 through DO36) are potentially available depending on the instrument’s model number.

Video Recorder – User Manual 65