GENERAL DESCRIPTION
The Apollo Intelligent Thermistor Meter (IMY) accepts standard Thermistor inputs and precisely linearizes them into temperature readings. Like an RTD, a thermistor is a temperature sensitive resistor, but the thermistor provides a much larger resistance change per degree. Since thermistors provide a large resistance change, significant errors from long lead lengths or switches are eliminated. Other advantages of using a thermistor are accuracy, repeatability, long term stability, and sensor cost. A full 6-digit display accommodates a wide range of temperature inputs and holds large totalization values. State-of-the-art digital circuitry virtually eliminates errors due to drift. A full complement of option packages is available to fulfill many process applications.
The IMY supports two popular thermistor series - the 400 Series 2,252 Ohm thermistor, and the 700 Series Thermolinear thermistor. Selection between the two types is done in Programming Module 1.
The indicator features a readout choice of either Fahrenheit or Celsius with
0.1or 1 degree of resolution. English Style display prompts aid the operator through set-up and operation. A front panel lock-out menu protects set-up data and operation modes from unauthorized personnel. Programmable digital filtering enhances the stability of the reading. Programmable remote input “E1-CON”pin can be utilized to control a variety of functions, such as totalizing, alarm control, peak/valley reading, display hold or offset operations. All set-up data is stored in the E2PROM, which will hold data for a minimum of 10 years without power.
An optional integrator/totalizer can be used to totalize or integrate temperatures up to a maximum display value of 999,999. It features independent scaling and a low temperature cut-out to suit a wide variety of temperature integration applications. A programmable remote input, “E2-CON”, is included with the option and can be utilized to control a variety of functions, such as totalizing, alarm control, peak/valley readings, display hold or offset operations, simultaneously with the “E1-CON”. Peak/valley (max/min) reading memory functions are included with this option and they are easily recalled and controlled by either the front panel or a remote input. All readings are retained at power-down.
Optional dual relays with parallel solid state outputs are fully programmable to operate in a wide variety of modes to suit many control or alarm applications.
Optional 20 mA loop, bi-directional serial communications provides computer and printer interfacing to extend the capabilities of the indicator.
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More than one unit can be connected in the loop with other RLC products which have serial communications capabilities.
An optional 4 to 20 mA or 0 to 10 VDC re-transmitted analog output can be scaled by the user to interface with a host of recorders, indicators and controllers. The type of analog output is determined by the model ordered. (See Ordering Information for available models.)
The indicator has several built-in diagnostic functions to alert operators of most malfunctions. Extensive testing of noise interference mechanisms and full burn-in make the indicator extremely reliable in industrial environments. The die-cast front bezel meets NEMA 4/IP65 requirements for washdown applications. Plug-in style terminal blocks simplify installation wiring and change-outs.
THEORY OF OPERATION
The IMY employs a microprocessor to perform the A/D conversion on the input signal via a voltage-to-frequency converter. It digitally scales the result, corrects for meter drift which may be present and then displays the result in a 6-digit display (4 digits for temperature, 6 digits for totalizer). The inputs are filtered to enhance the stability of the display. A non-volatile E2PROM provides permanent data retention for operating variables. The display consists of drivers and 6-digit solid-state LEDs. The alarm option employs opto-isolators to isolate the open collector devices from meter common. Operating in parallel, the relays are type Form-C and are rated at 5-amps. The serial communication option features a built-in 20 mA current source and complete opto-isolation. The analog option features a 12-bit DAC and provides a 4 to 20 mA or 0 to 10 VDC output that is digitally scaled. The analog output is isolated from meter common.
