MS-202 / PS-IN202 Wiring Guide: 4-Pin Load Cell Connector & RS-232
- pete8781
- Jul 29
- 2 min read
For MS-202 wiring, connector or replacement help, call MNM Scales at (832) 290-3120 or email mnmscales@yahoo.com.
The MS-202 / PS-IN202 wiring guide starts with the load-cell bridge, because a correct connector shape is not enough to guarantee correct polarity. The PS-IN202 documentation identifies red as +Excitation, black as -Excitation, green as +Signal and white as -Signal for the standard four-wire connection. Always verify the actual platform or junction-box wiring before applying power to a replacement indicator.
What Excitation and Signal Wires Do
Excitation powers the strain-gauge Wheatstone bridge inside the load cell. Signal wires return the small differential millivolt output created as force changes the bridge. Reversing excitation can change polarity; reversing the signal pair can make weight move in the wrong direction. A dead, unstable or saturated reading can also come from an open conductor, shorted shield, wet junction box or wrong connector pin assignment.
Four-Pin Platform Connection
The PS-IN202 family uses a four-pin platform connection in common configurations. When replacing an indicator, record the old connector pin assignment before disconnecting it. If the new indicator uses the same style of connector, still verify pin-to-function continuity because different scale brands may wire identical-looking plugs differently. On a four-load-cell floor scale, the individual sensors usually join in a summing/junction box first and a single four-wire cable continues to the indicator.
RS-232 Printer and Computer Connection
MNM lists printer and continuous data output, while PS-IN202 documentation describes full-duplex RS-232 communication. RS-232 is useful for weight tickets, external logging, custom software or a compatible remote display. Correct serial communication requires more than plugging in a cable: the connected device must use compatible baud rate, data format, parity/stop-bit settings and transmit/receive wiring. If no data arrives, check those settings before assuming the indicator port is defective.
Troubleshooting a New Indicator Installation
If the display moves negative when weight is applied, recheck signal polarity. If it does not move, verify excitation is reaching the platform and inspect continuity through the signal pair. If weight jumps when the cable is touched, inspect damaged conductors and shield termination. If one corner differs on a multi-cell floor scale, diagnose that load cell, mounting foot and junction-box trim before recalibrating the entire indicator.
After Rewiring, Recalibrate
A replacement indicator or changed load-cell connection normally requires calibration and verification. Use the documented P11 zero and P12 span routines only after wiring and mechanical response are stable. The related calibration guide walks through the sequence and verification steps.
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