JH1800: Single Trip Alarm
JH1820: Dual Trip Alarm

  • Potentiometers from 100 ohms to 100Kohms
  • Offset and Expanded Input Ranges
  • Switch-Selectable HI/LO Trip Function
  • Adjustable Deadband Standard
  • Uses Standard 11-Pin Socket
  • AC or DC Power Options




Models JH1800 and JH1820 monitor the position of a potentiometer or slidewire wiper and provide relay contact HI/LO trip outputs. Both are fixed-range devices: you may specify 0/100% input travel or any expanded range covering a 10% or wider portion of the travel.

The alarm trip points are adjustable anywhere within the input range. Deadbands also are fully adjustable, from 0.25% to 100% of span. A slide switch, accessible through the top of the enclosure, selects HI or LO trip operation (on dual alarms, HI/HI, HI/LO or LO/LO). Red/green LEDs indicate alarm status.

Alarm contacts are rated at 5 amps, 230Vac or 30Vdc. Model JH1800 provides one set of DPDT relay contacts; Model JH1820, two SPDT relays. AC and DC power options are available.


Model Number:  Select JH1800 single-trip alarm or JH1820 dual-trip alarm. Add suffix –AC for AC power or –DC for DC power.
Input Potentiometer:  It is not necessary to specify the potentiometer’s resistance. Just make sure it is no less than 100 ohms nor more than 100Kohms.
Input Range:  Specify 0/100%, or any 10% or wider portion of the travel (for example, 60/70%).
Trip Point:  If you would like the trip points to be factory set, please specify the following for each trip point. Specify HI or LO trip, specify the setpoint and specify the amount of deadband required (or specify "minimum deadband").
Relay Action:  Standard is Failsafe - the relay is energized under normal conditions and deenergizes upon alarm or upon loss of power. Thus, loss of power is seen as an alarm condition. Or specify Option R (Reverse Acting) – relay is normally not energized and energizes (pulls in) upon alarm trip. Failsafe is provided if not specified.
Power:  Specify 115Vac, 230Vac, 12Vdc or 24Vdc.
Urethane Coating:  

Specify Option "U"


These alarms plug into any standard 11-pin circular ("octal") relay socket. JH Technology offers a socket suitable for DIN-rail or surface mounting (see the Accessories page). Pin connections are:

Pin 1: Power (AC or, if DC power option, DC plus). 
Pin 2:
Potentiometer clockwise (or 100%) end connection. 
Pin 3:
Power (AC or, if DC power option, DC minus). 
Pin 4:
Potentiometer counterclockwise (or 0%) end connection. 
Pin 5:
Potentiometer wiper. 
Pin 6:
Setpoint 1 relay NO contact.* 
Pin 7:
Setpoint 1 relay moving contact.* 
Pin 8:
Setpoint 1 relay NC contact.* 
Pin 9: Setpoint 2 relay NO contact.* 
Pin 10:
Setpoint 2 relay moving contact.* 
Pin 11:
Setpoint 2 relay NC contact.*

  • Notes: NO (normally open) and NC (normally closed) refer to the relay state when no power is applied. For Failsafe operation the NO contacts are closed under nonalarm conditions. The NC contacts close upon alarm and upon loss of power. The terms Setpoint 1 and Setpoint 2 refer to dual-trip alarms. For single-trip alarms, both sets of contacts respond to the one trip point.


Input Potentiometer:  May be any resistance between 100 ohms and 100Kohms. It is not necessary to specify the potentiometer resistance on your order: end-to-end resistance does not affect the calibration.
Input Capabilities:  0 to 100% travel, or any 10% or wider portion of the travel (for example, 35/45%).
Relay Contacts:  Single Alarm, one DPDT relay. Dual Alarm, two SPDT relays. Contacts rated 5 Amps resistive, 115/230Vac or 30Vdc. 1/8 HP max inductive load at 115/230Vac. Refer to instructions for contact protection when switching inductive loads.
Setpoint Adjustment:  0% to 100% of range.
Deadband Adjustment:  0.25% to 100% of range.
Response Time:  under 100 milliseconds.
Isolation:  Input is isolated from power and from relay contacts. 1,500Vac rms (2,100V peak) breakdown.
Guaranteed Operating Temperature:  -10 to +60 deg. C (14 to 140 deg. F).
Temperature Stability:  +/-0.02% of span per deg. C, or better.
Power Requirements:  AC, 115 or 230Vrms, 50/60 Hz., 2.5V-A. DC, 12 or 24Vdc, 2.5W.