For a downloadable version of this page in PDF format please click on 4848 4838 Reactor Controller FAQ.
Software – How do I connect to PC?
This requires an A1925E2 or A1925E4 RS-485 conversion cable and a spare USB slot on the PC. See the 4848 Instruction Manual 548M or the 4838 Instruction Manual 551M for detailed instructions.
Most troubles with connecting to the controller through the PC are a result of a bad driver installation, or not locating the proper COM port. The driver installation should be done from the enclosed CD. The COM port may be located by going to the Device Manager on the PC and looking for the active COM port connected to the controller.
Software – My Recording file cuts out after a period of time
Check the power settings on the PC to ensure that it never hibernates, shuts off the hard drive, or shuts off the USB connection. Unfortunately, it’s tough to check whether the PC shuts off the USB connection or not. Perhaps the easiest test is to install the A1925E2 or A1925E4 RS-485 conversion cable on a different PC to see if it works properly there.
If the problem persists, it is likely a faulty A1925E2 or A1925E4. Contact Parr Technical Support for confirmation.
Software – How do I change the set point?
The controller can be locked out such that the PC cannot write to it. Ensure that the “Com Write” is set to Enable, and then click on the SV value to change it.
On the Motor Control Module, the setpoint is offset by a factor of 10. That is, if you want an rpm setpoint of 100, put in a value of “10”. The software will display the correct value after it is entered.
On the Pressure Display Module, the setpoint is offset by a factor of 10 when operating in psi units (so input “10” for a pressure alarm setpoint of 100). When operating in bar, there is no offset.
The Monitoring program which is used to change setpoints cannot be accessed when running the Datalogging program. However, the setpoints can be changed from the physical controller at any time, or the temperature programmer could be used instead.
Primary Temperature Meter – Displays “No Cont”
The meter is not sensing an input signal. This is most commonly due to plugging in the thermocouple into the wrong input jack, a faulty thermocouple, or faulty extension wire.
The wrong input jack can be checked by moving the extension wire from one jack to another.
A faulty thermocouple can be checked by unplugging the thermocouple extension wire from the thermocouple and shorting the wire using a paper clip or other suitable conductor. Leave the extension wire plugged into the Primary Input jack. The Primary Temperature meter should read a temperature somewhere close to room temperature when shorted.
A faulty extension wire can be checked by unplugging the extension wire from the controller and shorting the input jack using a paper clip or other suitable conductor. The Primary Temperature meter should read a temperature somewhere close to room temperature when shorted.
If none of these measures cause the “No Cont” error to go away, check the controller settings using a the defaults in the back of the manual. If this doesn’t clear the error, open the controller and check that the internal thermocouple wire from the Primary Input jack is connected to the Primary Temperature meter (white wire to pin 4 and red wire to pin 6).
Primary Temperature Meter – My controller won’t heat
Check that the High Limit Alarm isn’t tripped. Also, the heater switch should be in Position 1 (low power) or Position 2 (high power). After this, make certain the Primary Temperature meter is in Run mode (press the Return key) and set “R-S” to “Run”.
Motor Control Module – My stirring speed oscillates before reaching setpoint
The MCM uses a PID algorithm to control the stirring speed. The PID settings are such that the oscillations should clear within 60 seconds. However, this has the side effect of winding up if the controller is on for a period of time with either the Local/Remote switch in Local mode, or with the Motor power switch Off. This results in a big burst of power when switch is flipped and the motor is engaged.
One solution is to leave the Local/Remote switch in Remote mode and leave the Motor power switch in the On position all the time. That way when you turn on the controller it will automatically try to turn the motor and the windup will be eliminated.
Another solution is to leave the Local/Remote switch in Local mode at first. When you turn on the Motor power switch, use the knob to bring the stirring speed to somewhere slightly above (but not below) the MCM setpoint and let it sit for a few minutes. Then change the Local/Remote switch to Remote. This will cause the motor to undershoot the setpoint and then come back up slowly.
Also, the controller could simply be operated in Local Mode.
Motor Control Module – My stirring speed won’t reach the setpoint
The MCM can only go as high as the pulley will allow. Most bench top reactors are equipped with pulley that allows a maximum stirring speed of 600 rpm. This allows the motor to deliver more torque, but limits the maximum speed. High speed pulleys up to 1700 rpm are readily available.
Pressure Display Module – stuck at Zero (or some other fixed number)
This could mean the display constantly shows Zero or some other fixed value (such as 242 or 62) regardless of the actual pressure. The “non-zero” fixed value occurs in later pressure meters which have a fixed non-zero baseline voltage in the controller module itself.
This occurs because the Pressure Display is not getting an input signal. This could be because of a faulty harness, faulty transducer, or bad wiring connection.
A faulty harness is almost never a problem, but it can be checked with an ohmmeter for connectivity.
A faulty transducer can only be checked by trying a known good one.
A bad wiring connection typically occurs when the connection to the excitation board pops out in shipping. You can check the wiring visually from the back of the Pressure Input receptacle.
Connection 1 goes from the Pressure Input to the back of the Pressure Display Module (white wire to pin # 4 and black wire to pin # 6)
Connection 2 terminates in a black tab on the excitation board. This tab that sometimes pops off in shipping.
This tab can be reconnected by hand. There are multiple pin locations; any of them should work. It is possible for one of the sets of pins to be faulty and the others function; if one set doesn’t work, try another.
Be certain to orient the tab such that the black wire is closet to the outside of the excitation board.
An overall diagram of the wiring for the pressure display is shown below.
Setting up a Ramp and Soak Temperature Profile
The controller is typically operated in setpoint mode, where it simply attempts to maintain the desired setpoint. In some cases, it is desirable to input a ramp and soak profile. An example is shown below:
Note that Step 0 is a soak step by default. It is useful to think of subsequent steps as all “ramp” steps, but some with a temperature slope of zero (and therefore a “soak”).
Instructions for accessing the programmer can be found in the 548M 4848 Reactor Controller Instruction Manual.
High Limit Alarm is tripped
The High Limit Alarm is a breaker that interrupts power to the heater. When it trips, no power can flow to the heater, and the indicator will light up. The High Limit Alarm should only trip when the 4848 senses an alarm condition. The conditions are:
Interrupted thermocouple connection
This can be tested by wiggling the thermocouple and extension wire. Check to see if the display changes when doing this. If at any point the temperature display gives an error or an unrealistic temperature, it is safe to assume the trouble lies with a faulty thermocouple or faulty extension wire.
A faulty thermocouple can be tested by unplugging the extension wire from the thermocouple, and shorting the two ports on the end using a paper clip to simulate a temperature around room temperature.
A faulty extension wire can be tested by unplugging the extension wire from the back of the controller and shorting the two ports on the thermocouple jack with a paper clip to simulate a temperature around room temperature.
This could be the thermocouple on the Primary Temperature, or on the HTM or ETLM if present.
Interrupted pressure connection
This can be tested by checking cable connection or watching display to see if it changes spontaneously. See FAQ section on “Pressure Display Module”
Temperature exceeds alarm setpoint
Check the value of AL1.H by pressing return key three times on the Primary Temperature Meter. This represents the alarm temperature for the main thermocouple. If the thermocouple senses a temperature beyond this alarm temperature, it will trip the High Limit Alarm.
If an HTM is present, check the value of the setpoint on the main screen to ensure it has not been exceeded.
Pressure exceeds alarm setpoint
Check that pressure is not above shown setpoint on the main screen.
If none of these conditions are apparent, it might be a faulty High Limit breaker. This is a very rare problem, but it does occur occasionally. Typically when this happens, pressing the button for the breaker back in will feel rough or be difficult to do by hand.
Temperature Overshoot – My temperature overshoots the set temperature
Temperature overshoot is a common occurrence in systems with the following features:
- A long thermal lag between the heater and thermocouple
- A heating element designed for much higher temperatures than the set temperature
Unfortunately, pressure vessels by design tend to have both of these features. Overshoot tends to be most pronounced when trying when the set temperature is below 150C. Most Parr reactors are designed for use up to 350C and beyond, so control at lower temperatures can be troublesome.
Fortunately, there are a number of measures that can be taken to reduce or eliminate the overshoot.
An autotune may be used to adjust the control parameters in the controller to give better control with less overshoot and less oscillation around set temperature. See the 548M (4848 manual) or 551M (4838 manual) for instructions on how to autotune.
The 4848 and 4838 controllers tend to autotune well at temperatures above 150C in our reactors. During the autotune, the controller heats at 100% power for a while and watches the temperature rise. Then it heats at 0% power and watches the temperature drop. It will then repeat a few times.
If it takes too long for the temperature to drop after the first step, the autotune algorithm thinks it is taking too long and aborts the autotune. If this occurs in an autotune near 150C, try blowing a fan on the vessel to increase heat dissipation and retry the autotune.
Autotuning at temperatures much below 125C are typically not successful, fan or not.
Fundamentally, overshoot tends to occur because the system is taking in more heat than it can dissipate at the set temperature. Blowing a fan on the vessel will increase the heat dissipation. This is more effective at higher temperatures where overshoot tends to only be a few degrees. A typical setup would have the fan blowing on the vessel as soon as the run is started, or once the temperatures gets to within about 25C of the set temperature.
If the vessel is equipped with an internal cooling coil, water cooling may be used. Water cooling increases the heat dissipation, and to a much greater degree than fan cooling.
One typical water cooling setup would entail attaching a water line to the cooling coil and passing it through a needle valve so the water flow is not so fast that it overcomes the heater altogether. Water would flow through the cooling coil during the entire heat-up, which has the unfortunate side effect of increasing the heat up time.
A superior option is to attach a Solenoid Valve Module to the cooling coil at the inlet. These SVM’s are available at a modest cost and are usable with the 4848 controller (but not the 4838). When using an SVM, you can program the 4848 controller to turn the cooling on when the temperature breaches a certain point. It is advisable to make this point significantly below the set temperature.
The default controller values on the 4848 are designed to suppress exothermic reactions, not suppress overshoot, so the settings should be modified as such:
CoEF = 1 (Proportional band multiplier)
dEAd = -20 (dead band)
Here -20 is the point below set temperature where cooling kicks in. So if the set temperature were 100C, cooling would kick in at 80C. This value may be adjusted after a test run to see if overshoot continues. See the 548M manual for instructions on changing the controller values.
If feasible, using a lower wattage heater addresses the fundamental problem that the heater is overpowered for the application. One good rule of thumb says to design the heater such that the intended operating temperature may be maintained with 50% power. The standard Parr heater probably only needs 20% power to maintain 150C, and less for lower temperatures.
For overshoot suppression, nothing beats an oil bath or circulator. These heating devices are designed such that overshoot is basically impossible. If the temperature to be maintained is low enough, even a water bath/circulator may be used. Circulators would require a jacketed cylinder.