GF Signet 9900 & 9950 Transmitters + Add-On Modules
Single-channel (9900) vs. multi-channel (9950) transmitters, and all six real field-installable add-on modules — spec’d for process instrumentation in high-purity and semiconductor water systems.
The GF Signet 9900 is a single-channel transmitter handling one parameter; the 9950 supports up to six sensors, with two channels active in the base unit. Six field-installable modules extend the 9900: relay, batch, direct conductivity/resistivity, H COMM (HART), 4-20mA output, and PC COMM. Control-system links use HART or, on the 9950, an optional Modbus RTU module.
Single-Channel vs. Multi-Channel: Which Transmitter Fits Your Process
The 9900 is a single-channel transmitter — one instrument, one parameter. The 9950 supports up to 6 sensors, same or different type, in one instrument, with a base unit that ships already covering 2 channels. Choose based on how many measurement points you actually need to consolidate at one panel, not just on price.
| Model | Channels | Parameters | Display | Power |
|---|---|---|---|---|
| 9900 | Single-channel | Flow, pH/ORP, Conductivity/Resistivity, Salinity, Pressure, Temperature, Level, Dissolved Oxygen, or any 4-20mA sensor — one parameter per unit | 3.90" x 3.90" backlit dial-type digital bar graph, 7/14-segment | 12–32 VDC (24 VDC nominal), loop-powerable, 200mA (300mA with relay module) |
| 9950 | Two to six channels | Up to 6 sensors of the same or different type in one instrument, base unit ships with 2 channels/2 outputs | Split-screen CH1/CH2 display, each independently configurable | Same power class as 9900; optional dual-output modules expand to 6 total 4-20mA outputs |
Specifications sourced from GF Signet's own 9900 and 9950 transmitter datasheets. Verify current documentation and exact configuration before purchase.
All 6 Real GF Signet 9900 Add-On Modules
Every module slides into the back of the 9900 base unit, secures with a screw, and can be added or replaced at any time without replacing the main transmitter.
Relay Module
Adds two programmable dry-contact relays (relays 2 & 3) with hysteresis and time-delay settings.
Batch Module
Adds batch capability to 9900 Gen II — stores up to 10 batch sizes with custom names and K-factors, relay-mode batch control, source-volume monitoring.
Direct Conductivity/Resistivity Module
Interfaces GF Signet 2819–2823 and 2839–2842 conductivity electrodes directly to the 9900, with conductivity/resistivity/salinity readout and cable-length extension to 30m (100ft).
H COMM (HART) Module
Enables HART protocol communication — digital signal superimposed on the 4-20mA loop — for remote access to primary/secondary measurements and remote 4/20mA adjustment without physically accessing the unit.
4-20mA Output Module
Adds a second isolated 4-20mA output (base unit ships with one).
PC COMM Configuration Tool
PC-based configuration and diagnostic tool for the 9900 series — save and transfer device configurations.
Pricing pulled from named distributor listings (Instrumart, Cole-Parmer) at time of research — confirm current pricing before ordering; distributor pricing changes without notice.
Connecting the 9900/9950 to Your Control System
If your process instrumentation needs to talk to a PLC or SCADA system, the H COMM module enables HART protocol communication over the existing 4-20mA loop — useful for remote calibration and diagnostics on sensors located in hard-to-reach sub-floor or cleanroom locations without a technician physically accessing the unit. The 9950 also supports an optional Modbus RTU module for RS485 communication. Confirm which protocol your existing control system speaks before ordering either.
9900/9950 Transmitter & Module FAQs
What's the difference between the GF Signet 9900 and 9950 transmitter?
The 9900 is a single-channel transmitter — one instrument, one parameter (flow, pH/ORP, conductivity/resistivity, level, etc.). The 9950 is a multi-channel transmitter supporting up to 6 sensors of the same or different type in one instrument; the base unit ships with 2 channels displayed simultaneously (CH1/CH2), each independently configurable, with optional dual-output modules expanding to 6 total 4-20mA outputs. The 9950 also adds derived functions (sum, delta, ratio, % recovery, % reject, % passage) and advanced boolean relay logic that the 9900 doesn't have.
What add-on modules are available for the GF Signet 9900 transmitter?
Six real, field-installable modules: a Relay Module (adds two programmable dry-contact relays), a Batch Module (stores up to 10 batch sizes with custom K-factors), a Direct Conductivity/Resistivity Module (interfaces GF Signet 2819-2823 and 2839-2842 electrodes directly), an H COMM (HART) Module (remote calibration/diagnostics over the 4-20mA loop), a 4-20mA Output Module (adds a second isolated output), and a PC COMM Configuration Tool (PC-based setup and diagnostics). All slide into the back of the 9900 base unit and can be added or swapped without replacing the main unit.
Does the Direct Conductivity/Resistivity Module work with any GF Signet electrode?
It's built to interface GF Signet's own 2819–2823 conductivity/resistivity sensors and 2839–2842 PVDF electrodes directly, with cable-length extension to 30m (100ft) — verify the specific electrode series against the module's datasheet before ordering, since compatibility is electrode-family-specific, not universal.
Can the 9900/9950 communicate with a PLC or SCADA system?
Yes — via the optional H COMM (HART) module for HART-protocol integration, or the 9950's optional Modbus RTU module for RS485 communication. Which protocol to use depends on what your existing control system already speaks; confirm before ordering the module.
Where does GF Signet's own literature explicitly name semiconductor or ultrapure water applications?
On the electrode side, not the transmitter side directly — GF Signet's 2818-2823 and 2839-2842 datasheets explicitly list "Semiconductor Water Production" and "Semiconductor" among named applications, and both product lines' operating-range charts label UPW (ultrapure water) and USP bands on the low-conductivity end of the measurement scale. The 9900/9950 transmitters themselves are parameter-agnostic instruments that display whatever sensor is wired in — the semiconductor-specific claim belongs to the sensors, not the transmitter housing.
Need the Right Transmitter/Module Configuration?
Send LibertyCES your channel count, parameter list, and control-system protocol — we'll verify 9900 vs. 9950 and the right module stack before you order.
Send James your spec
Fluid, concentration, temperature, flow or volume, and where it goes. James replies with a real answer, not a catalog page.
Reviewed by James Riggins, 30+ years specifying water and chemical process equipment · Updated