LP7515 / OP-902 Wiring Guide: 4-Pin Load Cell Connector & RS-232 Pinout
- pete8781
- Jul 29
- 2 min read
For connector or replacement-cable help, call MNM Scales at (832) 290-3120 or email mnmscales@yahoo.com.
LP7515 / OP-902 wiring questions usually fall into two groups: the four-pin quick-disconnect used for the load-cell signal and the DB9 RS-232 connector used for external communications. Correct pinout matters because reversing excitation or signal wiring can produce no reading, negative readings, unstable output or calibration errors.
Four-Pin Load Cell Connection
The related OP-902 documentation identifies the quick-disconnect functions as Pin 1 +Excitation, Pin 2 +Signal, Pin 3 -Signal and Pin 4 -Excitation. Always verify the connector orientation and exact cable assembly before rewiring. Load-cell wire colors vary by manufacturer, so map function to function instead of color to color unless the sensor documentation confirms the color code.
Connecting a Single Load Cell
A four-wire strain-gauge cell supplies +Exc, -Exc, +Sig and -Sig. Connect those functions to the corresponding four-pin cable/indicator lines. If force produces a negative value and the mechanical direction should be positive, the signal pair may be reversed; correct it using the documented wiring rather than changing calibration to hide a polarity problem.
Connecting a Four-Cell Floor Scale
A four-cell platform normally combines the sensors in a junction/summing box where corner-trim adjustments can equalize cell contribution. The junction-box home-run cable then connects to the LP7515. The manual family states the indicator can support up to four 350-ohm cells, but cable and junction-box wiring must still be correct.
DB9 RS-232 Pinout
The OP-902 manual identifies DB9 pin 2 as TXD/transmit, pin 3 as RXD/receive and pin 5 as ground. The documentation describes continuous send, manual send and command send modes. Communication settings such as baud rate must match the receiving device.
Troubleshooting Wiring Problems
No reading: verify excitation voltage and connector seating. Negative response: verify +Sig/-Sig polarity. Unstable reading when the cable moves: inspect strain relief and conductor continuity. Overload-style display with no physical overload: check load-cell connection and bridge condition. Before replacing the indicator, measure load-cell input/output resistance against its datasheet when possible.
Technical Manual
FAQ
Can I splice a load-cell cable?
It can be done with proper low-level signal practices, shielding and moisture protection, but a good connector or replacement cable is preferable when available because strain-gauge signals are small and sensitive to poor connections.
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