Hach 900 Section, Auxiliary Pin Assignments, Contact Closures, 4-20mA Input, Signal Description

Section 3

Table 2 Auxiliary Pin Assignments

Pin	Signal Description	Wire Color	Purpose	Rating
			This line is held at 5 V dc inside the sampler. When shorted to
			ground (Pin B), a signal is sent to the microprocessor inside the
			sampler causing it to “wake up” and begin or resume the sampling
	Liquid Level		program. It can be used in conjunction with a simple level float switch	24 V dc
			to actuate the sampler when liquid id present or to take over after a	(max) at
D	Actuator/Auxiliary	Black
			second sampler had finished its program. It may also be used with	100 mA
	Control Input
			any device (such as pH meter) which produces a dry contact output	(max)
			to control the sampler in response to some user defined condition
			(i.e. high or low pH); must be used in conjunction with Pin B
			(ground).
E	Special Output	Red	Normally at 0 V dc, this line switches to 12 V dc upon any of the	N/A
			selected event described in SECTION, PROGRAMMING.
			Normally an open circuit, this line switches to ground for 90 seconds
F	Program Complete	Green	at the conclusion of the sampling program. Used to “wake up”	N/A
	Output		another sampler to take over sampling or to signal an operator or
			datalogger upon the completion of the sampling program.

Note: The sampler provides 12 V dc on Pin A of the Auxiliary Receptacle and this voltage is pulsed back to Pin C each time the contact closes on the external flow meter. The external flow meter must provide a dry contact closure.

Note: Older model 4–20 mA interfaces (Cat. No. 913) require correct loop polarity to properly work. The newer generation

(Cat. No. 2020 series) interfaces are not sensitive to loop polarity.

Contact Closures

The sampler controller is capable of accumulating 1 to 9999 contact closures. Each contact closure output from a flow meter represents a specific flow volume.

Some flow meters have an adjustable output, i.e. one contact closure for every 100, 500, 1000, 10, 000 gallons of flow, etc., while others have a fixed output. In either case, the contact closure signal is sent more frequently for high flow rates, and less frequently for low flow rates. The sample frequency will increase as the flow rate increases and likewise, will decrease as the rate of flow decreases, thus taking samples in proportion to flow rate.

To connect the sampler to a flow meter, use Signal Cable (Cat. No. 940 or 540). To connect another brand of flow meter, use the Open-ended Signal Cable (Cat. No. 941 or 541). A contact closure input signal corresponds to Pins A and C on the Flow Meter/Auxiliary receptacle, and signal cable connector. The signal cable wires are white and yellow respectively. Polarity is not important unless the same closure signal is sent to more than one sampler.

4–20 mA Input

An optional interface unit is available (Cat. No. 2021) which converts a

4–20 mA flow meter output into a 12 V dc pulses. At 20 mA (100% flow rate), the interface sends ten pulses per minute; at 4 mA (0% flow rate), the interface sends zero pulses.

The interface has a 0.9 m (3 ft) cable with connector on one end, and a 3 m (10 ft) cable with two open wire leads on the other. Insert the connector into the sampler receptacle labeled “AUXILIARY”, located on the left side of the control housing. For the 3 m (10 ft) cable, the wire with clear insulation is POSITIVE (+) and the wire with black insulation is NEGATIVE (–).

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Auxiliary Connection	8544install.fm