3595-1Q1 - 20 Channel Analogue Reed Relay IMP




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Enhaced version of 20 Channel Analogue Reed Relay IMP which includes 3 and 4 terminal resistance and RTD measurement.

Environment of Use Indoor/Outdoor
Type of Logger Multicanal
Number of Channels 20
ADC Bits 20 bit

The 35951Q1 is an enhanced version of the 35951C1, which includes 3 and 4 terminal resistance and RTD measurement facilities organised in a similar way to the original 35951H IMP. All 20 channels are available to use in pairs for the 3 and 4 wire measurement modes.

The channels are fully programmable and so each 3 or 4 wire measurement takes up 2 channels but leaves the rest available for other 35951C measurement modes. It remains compatible with the 35951C, and the resistance measurement modes are programmed using the same codes as a 35951H. The connector wiring for the 3 and 4 terminal resistance modes differs a little from the 35951H , but otherwise the 35951Q is compatible with the measurement modes of the 35951H analogue channels.


  • Compatible Communications with 3595 series.
  • Compatible enclosure and connector blocks.
  • Thermocouple, resistance, RTD, voltage and current measurements in rugged enclosure.
  • 20 Channels per Module – precision reed relay isolation. Individually programmable.
  • Precision 3 and 4 wire resistance and RTD measurements. (35951Q1)
  • Enhanced 14 to 19/20 bit resolution. 100 to 10 measurements per second.
  • Enclosed connector blocks. Dual sensor accurate Cold Junction Compensation.
  • Thermocouple health monitoring Temperatures in ‘C or ‘F unit.


Number of channels / module: 20/10

Number of poles / channel: 3/6

Connector type input channels: Standard 3595 series, Isothermal Enclosure, Screw Terminals.

Measurement modes: V DC,  (mV DC, uVDC), Thermocouple, CJC temperature, Sensor health

Thermocouple types: K,J,T,R,S,E,B,N

Thermocouple compensation: Dual sensors

35951Q1 only: 3&4 wire resistance, 3&4 wire PT100

Measurement resolutions supported:                          

  • 19/20 bits at 9 measurements/s
  • 18/19 bits at 20 measurements/s
  • 17 bits at 30 measurements/s
  • 17 bits at 40 measurements/s
  • 15 bits at 80 measurements/s
  • 14 bits at 100 measurements/s

Number of bits includes sign counted as 1 bit.

50 Hz Mains frequency interference rejection is provided by 17 and 20bit mode.

60 Hz mains interference rejection is provided by 17,19 and 20 bit modes.

Higher Measurement rates possible by disabling drift correct measurements.

Voltage measuring mode

Input voltage ranges: +12V >-12V

                                        +2.0V >-2.0V

                                        +200mV >-200mV

                                        +30mV >-30mV

Automatic range selection is supported.

DC measurement accuracy  +/- 0.015% of reading + 0.01% of range + 4uV

Temperature coefficients DC voltage: 25ppm rdg + 0.1uV/ o C

Measurement sensitivity 30mV range 18 bits: <0.25uV

Additional error at 80 & 100/sec mode 0.03% of range

Current Measurement

Sensitivity ( 100R shunt fitted): <10nA

Accuracy as for voltage ranges + shunt accuracy


Resistance Measurement

Measurement configurations: 3 and 4 wire connection

Measurement Ranges: 2000 ohm, 256 ohm, 32 ohm

Sensing Current: <0.75 mA (switched)

Accuracy: 0.03% rdg + 0.015% rng +3 mohm at 18-20bits

Sensitivity @17bits: <1 mohm


RTD Measurement

PT100 -50 to 400 oC: +/-0.2oC

            -150 to 600 oC: +/-0.4oC

Measurement modes: 3 wire and 4 wire


Interference Rejection

AC 50/60Hz

Common mode rejection ratio channel group: <0.1uV/V

Single channel common mode rejection ratio: <1uV/V

Series mode rejection ratio 50 or 60 Hz +/- 0.05%: <1mV/V

Applies to 18,19,20 bit measurements.

DC channel common mode rejection ratio: <0.1uV/V

Maximum voltages operating:

Max. voltage between (+) and (-) inputs, same channel: +-12V

Maximum voltage between any two terminals: 200V

Note: reed scanners are not suitable for direct connection to power circuits


Overload Protection

Channel overload protection: Passive

                                                       50V continuous



For protection against transients and ground loops.

Isolation test voltage IMP to IMP or to SNET Tested at 500V


Power Requirement

Connector: Via SNET cable

Voltage: 11 to 48V

Current: <100mA at 12V, <50mA at 24V



SNET Interface: SNET standard compatible


Function: Power, Communication, ADC fault, Calibration error

Safety: EN61010-1:2010, EN61010-2-30:2010,

EMC: EN55011:2009, EN 61326-2-1:2006

Case size: 435*215*34.5mm

Protrusion of cable boots: 45mm

Weight: 3.23kg

Operating Temperature Range: -20 to 70oC

Relative Humidity(non condensing): 85% at 40oC

Vibration: 1g 10hz to 400Hz in 3 planes

Programming storage: Secure flash memory

Calibration temperature is 21’C

Thermocouple Measurement Accuracy

Internal Cold junction compensation errors included: (External compensation is also available)

Type                                  Range                                   Accuracy

K                                  -100 to 500                                  0.5oC

                                      500 to1200                                 0.7

                                    1200 to 1600                               3.0

J                                      -50 to 360                                  0.5

                                      360 to 800                                  0.7

T                                   -150 to 400                                  0.5

R                                        0 to 1600                                2.0

S                                        0 to 1700                                 2.2

E                                     -50 to 290                                   0.7

                                      290 to 1000                                 1.0

B                                   200 to 1600                                 4.5

N                                 -200 to 1600                                  1.3

                                    -100 to 580                                    1.1 5

                                       80 to 1300                                  1.3

Displayed sensitivity: <0.1oC

Thermocouple Health Monitoring automatic by resistance measurement sequence.

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