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Model 9121 Two-Wire pH/ORP Transmitter
Click on part number above to request an RFQ or place an order online.

True 2-wire transmitter - reduces wiring and installation cost.
Input/Output isolated 4-20ma signal.
Corrosion resistant, waterproof NEMA 4X design.
May be retrofitted to most sensor installations.
Optional dual scale analog and digital meters available.
Any 1.4 pH (400mv) or greater fraction of input range expandable to full 4-20ma output.
Three operating modes - STANDBY, 0-14 pH, and EXPANDED allow startup and periodic calibration with readily available buffers and ORP standards.
Instruments for pH and ORP are identical except for meter scale, which simplifies spares for multiple loop installations.
The Model 9121 is designed to meet the need for an inexpensive, yet versatile, two-wire transmitter which produces a 4-20ma current output signal proportional to a pH or Redox input.
This high performance pH/ORP transmitter offers reduced installation cost due to its two-wire design. It can be supplied with the high impedance input stage mounted inside its case for direct electrode connection, or this portion of the circuit maybe removed and located nearer the sensor assembly.
Model 9121 provides a well isolated 4-20ma output signal compatible with common recorders, data loggers and most process control systems.
Three field selectable operating modes-STANDBY,0-14 pH (or ±2000mv), and EXPANDED - allow easy startup and calibration using standard buffers.
Continuously variable expansion (to x10) and zero suppression (to 14 pH units) capabilities allow any 1.4 pH or greater fraction of the input range to be expanded to a full 4-20ma output - yet electrode function can still be checked using standard buffers by simply switching to the 0-14 pH range. For example, a working range of 8.0 to 12.0 pH can be readily calibrated using 7.0 and 10.0 buffers without the need for unstable (and uncommon) high pH buffers.
As an ORP instrument, the versatile continuous controls allow expansion of any 400mv (or greater) span to 4-20ma.

SPECIFICATIONS
INPUT
Spans: Fixed 0-14 pH (±2000mv) plus an expanded range which is user adjustable for any span of 1.4 to 14 pH (400 to 4000mv) plus a standby position (4ma output).
Span Adjustment: Continuously adjustable noninteractive ZERO and EXPANSION controls. ZERO covers the complete input range.
Isolation: Greater than 60db (60 Hz AQ.
Withstanding Voltage: 130V AC or 200V DC.
Input Stage: Input impedance greater than 1 0 2Q, nominal bias current - 1 picoamp. Normally mounted inside instrument case, can be removed for external mounting a mile or more away.
OUTPUT
Standard: 4-20ma into 0-600‡, operating on 24V DC supply. Load resistances up to 12009 can be driven by increasing the supply voltage to 36V DC.
Optional Output Meters: Dual scale analog meter, 0-14 pH upper scale and 0-100% lower scale, accurate to within 2%, integrally mounted in case. A large (O.7") dual range liquid crystal display, 0-14 pH and 0-100% is available with user selectable resolutions of O.01 or O.1 pH (1 or10mv),and.1% or1% of span in the percent output range.
PERFORMANCE Repeatability: ±0.01 pH (±1 mv).
Linearity: 0.1% of span.
Accuracy: ±0.02 pH (±2mv).
OPERATING INFLUENCES
Temperature Coefficient: 0.001 pH/°C (±O.1 mv/°C).
Ambient Temperature Range: -30 to +60°C (-22 to +1 40°F).
Relative Humidity: Negligible influence.
POWER REQUIREMENTS
Standard: 24V DC supply, two-wi re, for 0 to 600Ω load. Can be as low as 1 2V DC for a maximum load of 109, 17V DC for 250Ω, and as high as 36V DC for 1200Ω. Instrument is not sensitive to power supply polarity.
CONSTRUCTION
Case: NEMA 4X construction of glass filled polycarbonate, no exposed metal hardware.
Conduit: Preformed knockouts for 1/2" and 3/4" conduit hubs.
Terminations: Two plug-in circuit card mounted terminal barriers for separate connections to 4-20ma loop (2 stripped 16 AWG to 24 AWG wires) and to preamplifier (4 stripped 16 AWG to 24 AWG wires).
Mounting: Wall mounting with four *6 screws or bolts.
Weight: 11/2 lbs. (680 gm).
Shipping/Storage: Non-operating temperature range is -30 to +85°C (-22 to +1 85°F).
Shipping Weight: 3 lbs. (1.4 Kg).

(Return to 2/Wire Transmitter)
	Model 9121 Two-Wire pH/ORP Transmitter Click on part number above to request an RFQ or place an order online. True 2-wire transmitter - reduces wiring and installation cost. Input/Output isolated 4-20ma signal. Corrosion resistant, waterproof NEMA 4X design. May be retrofitted to most sensor installations. Optional dual scale analog and digital meters available. Any 1.4 pH (400mv) or greater fraction of input range expandable to full 4-20ma output. Three operating modes - STANDBY, 0-14 pH, and EXPANDED allow startup and periodic calibration with readily available buffers and ORP standards. Instruments for pH and ORP are identical except for meter scale, which simplifies spares for multiple loop installations. The Model 9121 is designed to meet the need for an inexpensive, yet versatile, two-wire transmitter which produces a 4-20ma current output signal proportional to a pH or Redox input. This high performance pH/ORP transmitter offers reduced installation cost due to its two-wire design. It can be supplied with the high impedance input stage mounted inside its case for direct electrode connection, or this portion of the circuit maybe removed and located nearer the sensor assembly. Model 9121 provides a well isolated 4-20ma output signal compatible with common recorders, data loggers and most process control systems. Three field selectable operating modes-STANDBY,0-14 pH (or ±2000mv), and EXPANDED - allow easy startup and calibration using standard buffers. Continuously variable expansion (to x10) and zero suppression (to 14 pH units) capabilities allow any 1.4 pH or greater fraction of the input range to be expanded to a full 4-20ma output - yet electrode function can still be checked using standard buffers by simply switching to the 0-14 pH range. For example, a working range of 8.0 to 12.0 pH can be readily calibrated using 7.0 and 10.0 buffers without the need for unstable (and uncommon) high pH buffers. As an ORP instrument, the versatile continuous controls allow expansion of any 400mv (or greater) span to 4-20ma.
SPECIFICATIONS INPUT Spans: Fixed 0-14 pH (±2000mv) plus an expanded range which is user adjustable for any span of 1.4 to 14 pH (400 to 4000mv) plus a standby position (4ma output). Span Adjustment: Continuously adjustable noninteractive ZERO and EXPANSION controls. ZERO covers the complete input range. Isolation: Greater than 60db (60 Hz AQ. Withstanding Voltage: 130V AC or 200V DC. Input Stage: Input impedance greater than 1 0 2Q, nominal bias current - 1 picoamp. Normally mounted inside instrument case, can be removed for external mounting a mile or more away. OUTPUT Standard: 4-20ma into 0-600‡, operating on 24V DC supply. Load resistances up to 12009 can be driven by increasing the supply voltage to 36V DC. Optional Output Meters: Dual scale analog meter, 0-14 pH upper scale and 0-100% lower scale, accurate to within 2%, integrally mounted in case. A large (O.7") dual range liquid crystal display, 0-14 pH and 0-100% is available with user selectable resolutions of O.01 or O.1 pH (1 or10mv),and.1% or1% of span in the percent output range. PERFORMANCE Repeatability: ±0.01 pH (±1 mv). Linearity: 0.1% of span. Accuracy: ±0.02 pH (±2mv). OPERATING INFLUENCES Temperature Coefficient: 0.001 pH/°C (±O.1 mv/°C). Ambient Temperature Range: -30 to +60°C (-22 to +1 40°F). Relative Humidity: Negligible influence. POWER REQUIREMENTS Standard: 24V DC supply, two-wi re, for 0 to 600Ω load. Can be as low as 1 2V DC for a maximum load of 109, 17V DC for 250Ω, and as high as 36V DC for 1200Ω. Instrument is not sensitive to power supply polarity. CONSTRUCTION Case: NEMA 4X construction of glass filled polycarbonate, no exposed metal hardware. Conduit: Preformed knockouts for 1/2" and 3/4" conduit hubs. Terminations: Two plug-in circuit card mounted terminal barriers for separate connections to 4-20ma loop (2 stripped 16 AWG to 24 AWG wires) and to preamplifier (4 stripped 16 AWG to 24 AWG wires). Mounting: Wall mounting with four 6 screws or bolts. Weight: 11/2 lbs. (680 gm). Shipping/Storage: Non-operating temperature range is -30 to +85°C (-22 to +1 85°F). Shipping Weight*: 3 lbs. (1.4 Kg).