CA 34

Linearized RTD conditioners

General

The CA-34 Family Conditioners are isolated modules that enhance, filter, linearize, isolate, and convert to a level suitable for connection to the data acquisition system, Industrial PC, PLC or other measuring system with RTD (PT100) sensors.

Isolation conditioners of the CA-34 family protect people and measuring equipment and isolate galvanic from eventual events that may appear on the sensor side or somewhere else within a measuring environment. The module input is protected against voltage levels and transients up to 250 Vrms. Isolation voltage is 1500 V.

The CA-34 family of conditioners can be mixed with other families of isolation modules within the same application. They can be plugged into the measuring system and disconnected from it without turning off the power of the power or system shutdown (Eng. Hot swapable).

Prices and models of CA-34 Series

Attributes Linear Conditioning for PT100 or PT1000 RTD Sensor Triple insulation: input-output-supply 1500 Vrms Accuracy ± 0.1% Compliance to 100Ω RTD (Conformity) ± 0.025% 80 dB NMR for 50 Hz 160 dB CMR Power supply from 19 V to 30 V Voltage output: 0 ÷ 5 V; 0 ÷ 10 V, ± 5 V; ± 10 V, or Current output: 0 to 20 mA; 4 to 20 mA; ±5 mA; ±10 mA Input continuously protected from 250 V Transient protection according to ANSI / IEEE C37.90.1-1989 specification * The warranty period is 7 years, and the service period is 10 years

Simplified diagram of CA-34

Characterisation

The excitation current is passed through the RTD,  which causes a voltage drop depending on the current resistance of the RTD. This voltage is passed by a separate line (three wire connection) to the conditioner on which the voltage is measured by a chopper differential amplifier with low temperature drift, low offset and very stable gain coefficient. Differential amplifier does not require input grounding. On the front of the module there are two multi-turn trimmers for precise adjustment of the offset and the zero. Both values ​​are factory-set and the user can override them if there is a need for it.

Excitation for RTD is carried out using a 0.25 mA current source that minimizes self-heating of the sensor. The RTD linearization block is created to generate a nonlinear transverted function that is inverse with the specific non-linearity of the RTD sensor. Given specifications refer to a three-wire RTD connection. A two-wire connection is possible when a jumper is added between the terminals 1 and 2 as in the simplified diagram.

The central component of the module is a signal isolation transformer. Like most transformers, this has a primary and secondary side. Using this terminology, the input side of the module is the "primary side" and the output side of the module is called the "secondary side". A sensor connector is connected to the primary side of the module, and the secondary side of the module is connected to the data acquisition and measurement system, to the analog input module of the Industrial PC or PLC, to a panel meter or to another measurement system.

Transformer signal isolation uses a method of amplitude modulation to obtain linear, stable and reliable characteristics. This technique provides better results than the technique with digital or linear opto-scanners or a condenser isolation technique. The primary side of the module is galvanically isolated or "floating" in relation to the secondary side of the module and in relation to the power supply. The signal demodulator on the secondary side of the module restores the original signal, which is then filtered and buffered to achieve a low noise level and low impedance output signal.

The CA-34 Series Insulation Modules have a fifth-order filter built-in, with the first Anti-Aliasing filter located in the primary side, while the fourth-order butterworth filter is located on the secondary side of the isolation barrier. After the Anti-aliasing filtering, the signal is fed to the chopper level behind the specially designed micro transformer. In the secondary stage, behind the isolation barrier, the signal is demodulated and filtered again for the transmission noise and interference. The output from the module can be, optionally, a voltage or a current signal.

The warranty period is 7 years and the service period is 10 years. CA-34 is delivered with a user manual and with a calibration list.

CA-34 with 110/220V AC power supply (option)

The base version of the CA-34 works with a standard DC 19 to 30V DC power supply (24V DC nominal). However, if the application requires the power supply of a 220V AC coder, which is not a rare case, then the user can order a conditioner with the suffix A.

This type of conditioner works with an alternating voltage of 85 to 265V or with a DC voltage of 100 to 400V. These two power supplies make the CA-34 applicable in many situations. Some users use these conditioners in an environment that is powered by a 110V battery, or in elevated AC voltage conditions.

On this conditioner model, there are three terminals for connecting the power supply: L, N and GND (Picture on the left). The L should connect the phase, to N, and to the GND ground. Grounding, apart from the safety function, has the function of reducing the internal voltage unit oscillations, so it should be connected in any case. If the DC power supply is used, it must be connected to the L and N connectors (the schedule is not relevant).

Relay (option)

The family of isolating conditioners CA-34 with the suffix R has a built-in relay with a working and quiet contact on the external terminals. The relay can switch on or off to 240V, 6A, and can be set to activate when the input size is greater than the specified value or when the input size is less than the set value. There is a working and quiet contact on the copies. The relay has a built-in hysteresis control that can be fine tuned with a precision multi-port trimmer potentiometer.

The only limitation for this version is that if it is used with 220V power supply (version with suffix A), the relay has only a working contact.

The setting of the relay activation level is performed by the potentiometer on the front of the conditioner. In order to avoid the oscillation of the relay when the input size is the same, the hysteresis is assigned to the device. Hysteresis in the first case, when the relay is activated and when the input is greater than the set value, indicates the size of how much the input size should be smaller than the specified relay activation size for it to be turned off. In the second case, it indicates how much the input size it should be higher than the set to switch off the relay. Hysteresis can be set to 1% or 5% span with an internal jumper.

If the load is applied to the relay of the inductive character, it is necessary to add the "snubber" from the outside in parallel to the relay contacts. The values ​​of the supply components are calculated, but can also be determined empirically for the given application. Generally, even if the load is applied to the relay of the inductive type, a capacitor of 0.2 uF per line with a 10 Ohm resistor can be used. For optimum performance, the supply wheel must be calculated because this is the best way to optimally extinguish the spark at the relay.

Power supply and T-BUS connector

For the power supply of a smaller number of conditioners up to 20, a CS-24-48 that delivers 48W is recommended (picture on the left), and for greater number of conditioners a CS-24-90 of 90W should be used. Both models can, via the T-BUS connector be connected, directly, without wiring to power the conditioners on the same, or with the extension cable, on different DIN rails in a closed environment. This option raises reliability, greatly reduces the time of replacement of the conditioner and allows the conditioner to be connected or disconnected while the T-BUS is powered up.

Both power supplies work in a wide voltage range: CS-24-90 from 160V to 265V AC, while smaller, CS-24-48 can operate as much as 85V to 265V. If users do not want to use this type of power supply, they can also use other power supplies, but in this case, the power supply must be wired from one conditioner to the other by cables.

Picture on the left: Power supply CS-24-48 for conditioners with T-BUS connector