TM
INSTALLATION GUIDE
H738
OPERATION
The H738 is a current-sensitive switching device that monitors current (amperage) in
the conductor passing through it. A change in the conductor’s amperage that crosses
the adjustable switch threshold plus the hysteresis value causes the resistance of
the FET status output to change state, similar to the action of a mechanical switch.
In this model, the setpoint is adjustable through the action of a twenty (20) turn
potentiometer (see the CALIBRATION section). An integrated relay allows start/
stop control. The status output is suitable for connection to building controllers or
other appropriate data acquisition equipment operating at up to 30 volts. The H738
requires no external power supply to generate its output.
TROUBLESHOOTING
Problem
Solution
No Reading at Controller
• Check sensor calibration (see above)
• Check for control voltage at sensor (< 30 V)
• Check for amperage in monitored conductor (>1 A)
Setpoint screw has no
stops
The setpoint screw has a slip-clutch at both ends of its travel to
avoid damage. Twenty turns CCW will reset the sensor to be
most sensitive. Repeat calibration above.
Both LEDs are lit
Setpoint screw is too far clockwise. See solution above.
CALIBRATION
A. To monitor under-current (belt loss, coupling shear, status)
A
OK!
!
1. Turn setpoint screw
clockwise until Status OPEN
LED turns ON.
2. Slowly turn the screw counter-clockwise until the Status CLOSED LED just
turns ON.
3.Turn the screw an
additional 1/4 turn
counter-clockwise for
operational margin.
B. To monitor over-current (mechanical problems, seized impeller)
A
OK!
!
3. Turn the setpoint
screw an additional
1/4 turn clockwise for
operational margin.
1. Turn setpoint screw
counter-clockwise until Status
CLOSED LED turns ON.
2. Slowly turn the setpoint screw clockwise until the Status OPEN LED just turns ON.
OK!
STATUS
OK!
STATUS
Setpoint
Status
Open
STOP
Setpoint
Status
Closed
STOP
1/4
Setpoint
+
Setpoint
Status
Closed
STOP
Setpoint
Status
Open
STOP
+
1/4
Setpoint
Before beginning calibration, establish normal load conditions.
OK!
A
OK!
Then choose either A or B below.
4x
0.5A
DANGER: 5A CTs can present hazardous voltages.
Install CTs in accordance with manufacturer's instructions.
Terminate the CT secondary before applying current.
H68xx-5A CT
240A
300A:
5A
> 135 A (Sensor max.)
CAUTION
RISK OF EQUIPMENT DAMAGE
• Derate the product’s maximum current for the number of turns
through the sensing window using the following formula.
Rated Max. Amps ÷ Number of Turns = Max. monitored Amps
e.g. : 100A ÷ 4 Turns = 25 Amps max. in monitored conductor
• Failure to follow these instructions can result in overheating
and permanent equipment damage.
< 1 A (Sensor Min.)
NOTES
For load currents greater than sensor maximum rating:
Use a 5 Amp (H68xx series) Current Transformer (CT) as shown. This technique can be
combined with wrapping (see below) to add range for a low current load on a high
current source.
For load currents less than sensor minimum rating:
Wrap the monitored conductor through the center window and around the sensor
body to produce multiple turns. This increases the current measured by the
transducer.
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