Iwaki Metering Pump Wiring: Power, Pulse, STOP and Analog Signals

Most questions about Iwaki metering pump wiring concern the EHN series. Wiring this solenoid pump is not complicated once you split it into three parts: power, inputs (pulse, STOP, analog and FCM) and output (alarm). First check whether you have the EHN-R standard controller or the EHN-YN advanced controller, because they accept different signals. What follows is based on the controller specification in the Iwaki EHN catalog. Wire colors, terminal numbers and connector pinouts are in the instruction manual for your model, and we do not guess at what the catalog does not show.

EHN-R or EHN-YN?

The last part of the model code identifies the controller: R for standard, YN for advanced. Our guide to the Iwaki EHN model code shows how to read it.

• EHN-R: manual operation, external EXT pulse control (multiplication or division), STOP input, three keys.
• EHN-YN: everything on the R plus a 0-20 mA analog input, FCM flow check input, alarm output and sensor power supply, four keys.

If your control system will drive the pump with 4-20 mA, the R controller cannot do it. Specify the YN from the start, because that choice shapes all later Iwaki metering pump wiring.

Iwaki metering pump wiring: the power supply

Every EHN model runs on 100-240 VAC, 50/60 Hz, single phase, so it works on most mains supplies without a transformer. Average power draw is low: roughly 20 W for the BN drive and 24 W for the CN drive.

Two points on this part of Iwaki metering pump wiring:

1. Give the pump its own breaker or fuse so it can be isolated for service.
2. Make sure the earth connection is sound, and use residual current protection in damp dosing rooms.

Do not start and stop the pump by switching the mains. For remote on/off use the STOP input described below, which is much kinder to the controller.

Iwaki metering pump wiring for the pulse input

In EXT mode the pump strokes in response to external pulses. On both R and YN controllers the pulse input takes a voltage-free contact or open-collector signal. The input only needs to see closed or open; you do not supply voltage to it.

Typical signal sources:

• reed switch pulse output from a water meter or flowmeter;
• a PLC relay output;
• a PLC transistor output, provided it is open collector and wired with the polarity shown in the manual.

If the PLC output is a powered 24 V output, wiring it straight in can damage the input circuit. An interposing relay that turns it into a dry contact is the safe answer, and it is the single most useful tip in EHN pulse wiring.

Pulse multiplication gives n strokes per pulse; division gives one stroke per n pulses, with n set from 1 to 999. During multiplication, extra pulses are stored, up to 65535 shots. For general principles see 4-20 mA and pulse control for metering pumps.

Iwaki metering pump wiring for the STOP input

The STOP input is also a voltage-free contact or open-collector input. When the STOP signal is present the pump stops, and it resumes when the signal clears. According to the catalog, the action of the stop signal can be switched in the controller settings.

The classic use is a low-level switch on the chemical tank: when the level falls below the minimum, the switch operates and the pump stops before it runs dry. A PLC output can also be wired here for remote on/off. If you combine a level switch and a PLC output, decide on normally open or normally closed logic first, then set the controller to match. Getting this right is a core part of Iwaki metering pump wiring.

EHN-YN extras: analog, FCM and alarm

Iwaki metering pump wiring on a YN controller adds several circuits:

1. Analog input, 0-20 mA: a two-point setting maps current to stroke rate. For a 4-20 mA loop, simply set the 4 mA and 20 mA points.
2. FCM input: connects the optional FCM flow checker, an open-collector signal.
3. Sensor power, 12 VDC at 20 mA: intended to supply the FCM, not other loads.
4. Alarm output: a dry contact that can go to a PLC digital input or a beacon circuit.

The FCM fits below the pump inlet and confirms that each stroke draws liquid. If no flow is seen within the set time, the pump raises an alarm, runs at full speed for a while and then stops. Our article on EHN control panel settings covers the parameters.

Testing after Iwaki metering pump wiring

Do not go straight to automatic. Work through this order:

1. Run in manual mode to confirm power and the pump itself.
2. Switch to EXT and close the pulse contact a few times; the pump should stroke each time.
3. Trip the level switch and confirm STOP halts the pump and that it restarts when cleared.
4. On a YN, send several current values from the PLC and check that stroke rate follows the two-point setting.

Testing each circuit separately makes it obvious which part of the Iwaki metering pump wiring is wrong.

Common Iwaki metering pump wiring mistakes

Feeding a powered 24 V signal into the pulse or STOP input, so the signal is ignored or the input is damaged. Running the analog cable alongside power cables, causing erratic stroke rate; use shielded cable on its own route. Mismatched STOP logic, so the pump refuses to run with a normal tank level. Buying an R controller and then trying to connect 4-20 mA.

Conclusion

Correct Iwaki metering pump wiring starts with identifying the controller. The R has power, pulse and STOP; the YN adds analog, FCM, alarm output and a 12 VDC sensor supply. Pulse and STOP are voltage-free or open-collector inputs, so never apply voltage to them, set STOP logic in the controller, and take wire colors and terminal numbers from the manual. Explore more models on our Iwaki brand page and our solenoid metering pumps, and if you are unsure about a connection, contact our engineers with a photo.

FAQ

Can the EHN run on a three-phase 380 V supply?

Not directly. It is a single-phase 100-240 VAC pump, so take phase and neutral or use a transformer.

In Iwaki metering pump wiring, can a PLC transistor output drive the pulse input?

It depends on the output type. Open collector can be wired with the correct polarity; a powered 24 V output should go through an interposing relay.

Can an EHN-R be converted to 4-20 mA?

The R has no analog input. Analog control needs the YN controller; check with the supplier before any retrofit.

The pump will not run after connecting a level switch. Why?

Usually the STOP logic does not match a normally open or normally closed switch. Change the setting in the controller.

Can the alarm output drive a beacon directly?

It is a dry contact and can switch a beacon circuit, provided voltage and current stay within the contact rating given in the manual.